I have a number of v8.5 clients that are failing. The UpdateLog.txt says the following :-
09/04/2009 05:06:36 Domain\User Backing up file(s) Engine DAT 09/04/2009 05:06:59 Domain\User Pre-notifying for DAT update. 09/04/2009 05:06:59 Domain\User Copying DAT. 09/04/2009 05:06:59 Domain\User Update failed to version 5578.0000
Checking the Agent_ServerName.log gives the following :-
20090409050658 i #2684 Script Pre-notifying for DAT update. 20090409050658 i #6320 Script Copying DAT. 20090409050658 i #2684 Script Update failed to version 5578.0000
This seems to indicate an error with the sripting engine. McScript.log shows the following :-
Are you using McAfee Agent 4.0 Patch 1 on these machines?.
I ask because I had a similar issue. Working with McAfee this was finally resolved by updated to McAfee Agent 4.0 Patch 2. Since this was deployed to the clients, all systems have updated successfully.