Try the following steps to resolve this issue.
Check your visual studio 2012 is up to date with service packs. If you have not updated with Service pack update 3 or by now it should 4, you may see this issue.
Go to HELP -> About Microsoft Visual Studio and check for the version you have.
If you do not see it with update 3 or above then, go to TOOLS -> Extensions and updates in Visual Studio. Then click on Updates -> Product updates.
You are not seeing any item in my screen shot because my visual studio is up to date. But if you may see the latest update if your Visual Studio 2012 is not up to date. If you see any update then click on that to update your Visual Studio. This should resolve your issue.
2, If the first step did not work, then clean you build and then rebuild the solution. That should resolve your issue.