With SQL Server 2008 passing its 6 months since RTM date, a common problem is popping up in the forums and is now listed on Connect. When an install of Evaluation Edition Expires, the services stop functioning until an upgrade is made to a full version of SQL Server 2008. This is normal. The problem is that during the Edition Upgrade, SQL Server Management Studio is not upgraded, and a persistent popup will occur stating that the evaluation version has expired.
There is currently a workaround that can be done to resolve this problem. Open RegEdit and change the value of the CommonFiles REG_DWORD under the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\100\ConfigurationState registry from 1 to 3 and then rerun the Edition Upgrade. This will allow the Upgrade to Management Studio to complete properly.