Conflicting Versions of ASP.NET Web Pages Found

I am getting the following error when starting my ASP.NET web project:

Conflicting versions of ASP.NET Web Pages detected: specified version is "2.0.0.0", but the version in bin is "3.0.0.0". To continue, remove files from the application bin directory or remove the version specification in web.config.

The answer for this question solves this problem - in my Web.config

, switch

<add key="webpages:Version" value="2.0.0.0"/>

      

        
        
        
      

    

to

<add key="webpages:Version" value="3.0.0.0"/>

      

        
        
        
      

    

allows me to run my site successfully.

Unfortunately, a colleague who recently pulled out a clean copy of the repository gets the exact opposite error:

Conflicting versions of ASP.NET Web Pages detected: specified version is "3.0.0.0", but the version in bin is "2.0.0.0".

It can fix the problem by changing the value webpages:Version

to "2.0.0.0"

.

What is the cause of this error, and how are my colleague and I using the same version in our Web.config?