Strange false errors while compiling the Play / Activator program?

I have a large and moderately complex web application using the standard game stack, Scala and Akka. (I'm in the process of adding scala.js, but this issue precedes this.)

I upgraded to the current activator based version of the world a few months ago (lagging behind the times) and it mostly worked fine. But since then, I often get a strange error when I try to compile:

[Querki] $ compile
[trace] Stack trace suppressed: run last scalajvm/compile:compile for the full output.
[error] (scalajvm/compile:compile) java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt2595416303704565240.class (Access is denied)
[error] Total time: 3 s, completed Sep 2, 2014 3:26:43 PM

      

        
        
        
      

    

Once it starts, it usually repeats until I do a clean recompilation, so this is a pain in Tuchus. It takes some time to fully recompile the system, and this usually happens a couple of times a day. (OTOH, sometimes it just stops, seemingly for no reason.) Restarting the Activator doesn't help.

Does anyone know what's going on here? As far as I can tell, the classes.bak folder is created temporarily during the compilation process - I can see that it appears and then disappears again after the compilation is complete regardless of whether or not it succeeds. It definitely doesn't exist until the failed compilations begin. It seems that sbt is creating a temp folder in a crashed state or something.

If it matters, it runs on a Windows 7 box; I am using sbt 0.13.5, Scala 2.11.1 and Activator 1.2.10.

ETA: It's also possible that I'm thinking about it now - I'm also running GitHub for Windows. I mention this because it is a Java based application that clearly does something to periodically check for changes in the tree. (It automatically updates from time to time: whether the tree is scanning for changes or listening a la JNotify, I don't know.)

ETA2: Hah - finally remembered to print the full log before clearing. Here's the full stack trace: I don't know what to do with it, but maybe someone on the sbt side can use it:

[Querki] $ compile
[info] Compiling 1 Scala source to C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajs\target\scala-2.11\classes...
[info] Fast optimizing C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes\public\javascripts\querki-client-fastopt.js
[trace] Stack trace suppressed: run last scalajvm/compile:compile for the full output.
[error] (scalajvm/compile:compile) java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt1117112335838311075.class (Access is denied)
[error] Total time: 22 s, completed Sep 5, 2014 3:17:25 PM
[Querki] $ last scalajvm/compile:compile
scalajs/compile:compile
[debug]
[debug] Initial source changes:
[debug]         removed:Set()
[debug]         added: Set()
[debug]         modified: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala)
[debug] Removed products: Set()
[debug] External API changes: API Changes: Set()
[debug] Modified binary dependencies: Set()
[debug] Initial directly invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala)
[debug]
[debug] Sources indirectly invalidated by:
[debug]         product: Set()
[debug]         binary dep: Set()
[debug]         external source: Set()
[debug] All initially invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala)
[info] Compiling 1 Scala source to C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajs\target\scala-2.11\classes...
[debug] Getting compiler-interface from component compiler for Scala 2.11.1
[debug] Getting compiler-interface from component compiler for Scala 2.11.1
[debug] Running cached compiler 1f1ebd37, interfacing (CompilerInterface) with Scala compiler version 2.11.1
[debug] Calling Scala compiler with arguments  (CompilerInterface):
[debug]         -Xplugin:C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-compiler_2.11.1\jars\scalajs-compiler_2.11.1-0.5.4.jar
[debug]         -bootclasspath
[debug]         C:\Program Files\Java\jdk1.6.0_38\jre\lib\resources.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\rt.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\sunrsasign.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\jce.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\modules\jdk.boot.jar;C:\Program Files\Java\jdk1.6.0_38\jre\classes;C:\Users\jducoeur\.ivy2\cache\org.scala-lang\scala-library\jars\scala-library-2.11.1.jar
[debug]         -classpath
[debug]         C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajs\target\scala-2.11\classes;C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-library_2.11\jars\scalajs-library_2.11-0.5.4.jar;C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-dom_sjs0.5_2.11\jars\scalajs-dom_sjs0.5_2.11-0.6.jar;C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-jquery_sjs0.5_2.11\jars\scalajs-jquery_sjs0.5_2.11-0.6.jar;C:\Users\jducoeur\.ivy2\cache\org.webjars\jquery\jars\jquery-1.10.2.jar
[debug] Scala compilation took 6.133828284 s
[debug] New invalidations:
[debug]         Set()
[debug] Initial set of included nodes: Set()
[debug] Previously invalidated, but (transitively) depend on new invalidations:
[debug]         Set()
[debug] All newly invalidated sources after taking into account (previously) recompiled sources:Set()
scalajvm/compile:compile
[debug]
[debug] Initial source changes:
[debug]         removed:Set()
[debug]         added: Set()
[debug]         modified: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala, C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\app\qtext\LineParsers.scala)
[debug] Removed products: Set()
[debug] External API changes: API Changes: Set()
[debug] Modified binary dependencies: Set()
[debug] Initial directly invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala, C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\app\qtext\LineParsers.scala)
[debug]
[debug] Sources indirectly invalidated by:
[debug]         product: Set()
[debug]         binary dep: Set()
[debug]         external source: Set()
[debug] All initially invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala, C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\app\qtext\LineParsers.scala)
java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt1117112335838311075.class (Access is denied)
        at java.io.FileOutputStream.open(Native Method)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:194)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:145)
        at sbt.Using$$anonfun$fileOutputChannel$1.apply(Using.scala:82)
        at sbt.Using$$anonfun$fileOutputChannel$1.apply(Using.scala:82)
        at sbt.Using$$anon$2.openImpl(Using.scala:72)
        at sbt.OpenFile$class.open(Using.scala:46)
        at sbt.Using$$anon$2.open(Using.scala:70)
        at sbt.Using$$anon$2.open(Using.scala:70)
        at sbt.Using.apply(Using.scala:24)
        at sbt.IO$$anonfun$copyFile$3.apply(IO.scala:583)
        at sbt.IO$$anonfun$copyFile$3.apply(IO.scala:582)
        at sbt.Using.apply(Using.scala:25)
        at sbt.IO$.copyFile(IO.scala:582)
        at sbt.IO$.move(IO.scala:764)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2.sbt$inc$ClassfileManager$$anonfun$$anon$$move(ClassfileManager.scala:77)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2$$anonfun$delete$3.apply(ClassfileManager.scala:53)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2$$anonfun$delete$3.apply(ClassfileManager.scala:52)
        at scala.collection.immutable.HashSet$HashSet1.foreach(HashSet.scala:153)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:306)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:306)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:306)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2.delete(ClassfileManager.scala:52)
        at sbt.inc.Incremental$.prune(Incremental.scala:58)
        at sbt.inc.IncrementalCommon.cycle(Incremental.scala:96)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:38)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:37)
        at sbt.inc.Incremental$.manageClassfiles(Incremental.scala:65)
        at sbt.inc.Incremental$.compile(Incremental.scala:37)
        at sbt.inc.IncrementalCompile$.apply(Compile.scala:27)
        at sbt.compiler.AggressiveCompile.compile2(AggressiveCompile.scala:157)
        at sbt.compiler.AggressiveCompile.compile1(AggressiveCompile.scala:71)
        at sbt.compiler.AggressiveCompile.apply(AggressiveCompile.scala:46)
        at sbt.Compiler$.apply(Compiler.scala:75)
        at sbt.Compiler$.apply(Compiler.scala:66)
        at sbt.Defaults$.sbt$Defaults$$compileTaskImpl(Defaults.scala:770)
        at sbt.Defaults$$anonfun$compileTask$1.apply(Defaults.scala:762)
        at sbt.Defaults$$anonfun$compileTask$1.apply(Defaults.scala:762)
        at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
        at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:42)
        at sbt.std.Transform$$anon$4.work(System.scala:64)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
        at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:18)
        at sbt.Execute.work(Execute.scala:244)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
        at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:160)
        at sbt.CompletionService$$anon$2.call(CompletionService.scala:30)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:439)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)
[error] (scalajvm/compile:compile) java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt1117112335838311075.class (Access is denied)
[Querki] $