Mail Source Agent or other agent log cannot logon to the service mailbox. Could be the System Attendant or other service account that is failing.
The agent logs may reveal the following:
12/2/2011 3:07:47 PM CSession::Logon TraceMsg 4800 Logging on to the mailbox '/o=WET Automotive Group/ou=Odelzhausen/cn=Configuration/cn=Servers/cn=S11EXCH/cn=Microsoft System Attendant' (Server: 'S11EXCH', user: 'Domain\quest.mm', has assocciated PFDB: 'False', connection flags = 32768).
12/2/2011 3:07:47 PM CaeMAPISession::Logon TraceMsg 0 Trying to synchronize MAPI profile creation.
12/2/2011 3:07:47 PM CaeMAPISession::Logon TraceMsg 0 Creating MAPI profile.
12/2/2011 3:07:47 PM CSession::Logon Error -2147467259 Unspecified error File: 'aeMAPIProfile.cpp' Line: '132'
12/2/2011 3:07:47 PM CADQueue::NextItem TraceMsg 4514 No more items to process in this session.
The MAPICDO that is installed where the agent is located has become corrupted.
Reinstall the MAPCDO on that server where the agent is failing. Follow these steps accurately.
1. Uninstall existing MAPICDO.
3. Reinstall the new MAPICDO.
Typically found at Microsoft. http://www.microsoft.com/download/en/details.aspx?id=1004