Why was Jenkins unable to create the Play project because "routes are already defined as feature routes"?

I have a Play project that works fine on my MacBook but fails on a remote build server running Jenkins on Ubuntu Server 14. The build fails with the following error:

[info] Compiling 7 Scala sources and 120 Java sources to /var/lib/jenkins/jobs/<redacted-projectname>/workspace/target/scala-2.11/classes...
[error] /var/lib/jenkins/jobs/<redacted-projectname>/workspace/conf/routes: routes is already defined as object routes
[error] /var/lib/jenkins/jobs/<redacted-projectname>/workspace/conf/routes: routes is already defined as class routes
[error] two errors found

      

        
        
        
      

    

The same problem occurs on my local machine as well, but I just need to do ./activator clean

(or sbt clean

) and then it works fine.

Jenkins build profile is a directive Execute Shell

that executes the following scripts:

./activator clean dist

      

        
        
        
      

    

I tried to recreate the project by clearing the directory completely, but assemblies keep failing. Any help would be greatly appreciated.