You receive an error when you Right Click on any table and choose "Edit Top 200 rows"
Error - Invalid prefix or suffix characters. (MS Visual Database Tools)
This is known issue with SQL Server 2008 R2 Management Studio while connecting to SQL Server 2012.There are no claims on what features may/may-not work, and this is expected behavior.
There were errors in basic connectivity and those have been fixed in the past.
For example, http://support.microsoft.com/kb/2459027/EN-US (FIX: "Index was outside the bounds of the array" SMO error message when you connect to a SQL Server code-named 'Denali' CTP1 Database Engine instance in SSMS 2008 R2 and in SSMS 2008)
To use all features of SSMS, use the same version as MSSQL Server engine (i.e. MSSQL Server 2012 / MSSQL Server 2012 Management Studio Express)