Everyone got kicked out of Outlook this morning at 8:40

Exchange had a few System errors:

A process serving application pool 'MSExchangeMapiFrontEndAppPool' suffered a fatal communication error with the Windows Process Activation Service. The process id was '7812'. The data field contains the error number.

The Microsoft Exchange Transport service terminated unexpectedly.  It has done this 1 time(s).  The following corrective action will be taken in 5000 milliseconds: Restart the service.

We are non SP1 on CU3,  I'm looking to upgrade to CU8 soon... are there any other possible causes here?  

Is there an upgrade path from CU3 to CU8 that I need to take?

• Edited by JoeFri Friday, May 01, 2015 1:23 PM

CU8 Update completed, waiting for some time to confirm these issues don't return.