What version of ePO are you upgrading to, and which version do you have at the moment?
There'll be a mcafeelogs folder in the %temp% folder of the logged-on user - can you zip and attach the whole thing?
One of the main ePO extensions is failing to upgrade - I would open a case with Support for this as we're going to need to see full logs and so on.
We upgraded to EPO 4.6.6 last week & ran into the same problem. We got it working after disabling McShield & McAfee Framework services. The interruption was when McAfee EPO agent enforced the policy. Btw...make sure noboby log on to EPO server during your upgrade.