Cannot create new database diagram in SQL Server 2008

I'm using SQL Server Management Studio 2008 and SQL Server 2008. Currently, I cannot create new database diagram from the SSMS 2008 on an SQL Server 2008 instance. Has anyone ever experienced this ? The problem started after I tried to install Visual Studio 11 Beta, and apparently the Beta also installs SQL Server 2012 RC0. Now I have uninstalled the Visual Studio 11 Beta and the SQL Server 2012