Archiving Task failure to start EventID 3305, 2256

I'm having some issues getting my Exchange 2010 Mailbox tasks to start.

EV 9.03 and Exchange 2010 SP3

Upgraded Outlook 2003 to Outlook 2007 on EV server that handles Exc2010 tasks.

I've created all the system mailboxes on each MB server and placed them in the 1st database on the server (we have 4 on each).

I've run the Permissions script for Exchange, Throttling Script and a PS to apply Send As rights to each System Mailbox.

Deployment Scanner run through just now showed no issues (apart from the usual Lotus Notes - and we don't use it!).

I've looked at the following Technote with no success: enterprise vault EvtID=150585

Really stumped now and this is holding up EV deployment to our Exchange 2010 users.