Do you get error 435 in the Application event log and your SQLAgent fails to start? The reason you’re getting this error is that the SQLAgent error log and working directory file locations are not available.
I recently ran into this after moving the user and system databases to a different SAN drive. Even though you tell SQL where you moved MSDB, you still have not told it the new location for the error log and working directory. SQL stores these locations in the registry and you will have to update it. Here are the locations for the keys you need to update.
*** NOTE *** If you are on a cluster, make sure you update the registry on every node in the cluster.
HKEY_LOCAL_MACHINESOFTWAREMicrosoftMicrosoft SQL ServerMSSQL10_50.MSSQLSERVERSQLServerAgentErrorLogFile
HKEY_LOCAL_MACHINESOFTWAREMicrosoftMicrosoft SQL ServerMSSQL10_50.MSSQLSERVERSQLServerAgentWorkingDirectory
More Information – If you have this problem then you might want to check out the following posts: