I just encountered this problem, so thought id post it here for my future ref, and in case you find it, it may help..
You are running vs 2010 and 2012 side by side, you try and create a sql server db project in 2012 and get a "this project type is not supported", relating to the project type sqlproj..
To fix this, you just need to install sql server data tools for VS 2012. You can download them from the link below.. Hope it fixes your issue..
go to the link below and click the link "Download SQL Server Data Tools for Visual Studio 2012"