When doing a little bit of work on a solution that contains a Visual Studio Addin the other day, I noticed that there's a little bit of an issue with Visual Studio. If you create an addin project and you get the message:
An error occurred, and the wizard could not generate the project. Verify that the programming language is properly installed.
Then double check where you are creating your addin. If it is in a child folder of the solution, then this error can occur. The solution - add the addin project to the solution root. Then if you need to, you can move it afterwards.
This issue occurs in Visual Studio 2012, but a bit of googling suggests that it may also be an issue in 2010.