Double-check that you are not using a trailing backslash in your working directory path. We were and it was causing issues across modules (KBU/KAV/VSA) that have been resolved simply by removing that slash.
Hope this saves someone some time.
Quick and dirty way to check for offending paths in SQL:
SELECT I.machName + '.' + I.groupName AS Agent, agentTempDir AS PathFROM ksubscribers.dbo.users AS M INNER JOIN ksubscribers.dbo.machNameTab AS I ON M.agentGuid = I.agentGuidWHERE agentTempDir LIKE '%\'