Keep your system up to date with the most recent cumulative update package for SQL Server 2008 SP2. This package contains all of the SQL Server 2008 hotfixes that have been released since the initial release of SQL Server 2008 SP2.
Previous CU KB Articles:
Abhishek SinhaProgram ManagerSQL Server Sustained Engineering
FIX: An sp_execute_policy error if both SQL Server 2008 R2 and SQL Server 2008 are installed
This is fix that was released as part of CU7 for SP2, but is overridden if we upgrade the system to CU3 after this , which is kind of reintroducing the problem again after the upgrade.