What about Sql Server Data Tools for VS2012 being incompatible with Sql Server 2012?
Solution 1:
I Installed SQL Server 2012 Service pack 1 yesterday and then I started getting the problem you describe in Visual Studio 2012. Not only with database projects; I could not use the SQL Server Object Explorer, not open sql-scripts and lots of other weird database related errors. Always with the same message:
"This version of SQL Server Data Tools is not compatible with ... bla, bla, bla ..."
This solution helped me: https://web.archive.org/web/20150315060703/http://blog.wharton.com.au/2012/11/16/sql-server-2012-sp-1-breaks-sql-server-database-projects/ Hope this can help you too
Update: With the March 2013 Release it seems you have to also update the SQL Server Data Tools available here See the comments in this post for more details.
Solution 2:
Just downloading and installing the SQL Server Data Tools cured this for me;
http://go.microsoft.com/fwlink/?LinkID=274984
Solution 3:
This happened to me in visual studio 2012 on an existing project after I installed visual studio 2013. Installing the 2012 tools fixed it as others have said but the link provided in previous answers wasn't the one I needed. the link that did it for me is here