I've been suffering from update problems too over the last day or so. Same thing happened last year sometime IIRC. I'll give it a few days and then go back to Avast I think.

I upgraded an XP computer last Sunday to 8.5 (7.5 update said support was stopping on the 17th). Subsequent update ran without a problem. Haven't heard of an update issue since, but will check. (7.5 updates on 98SE/ME machines still working!).
An issue I have with that 8.5 upgrade is that Outlook is installed on that machine, but not used. Outlook Express used instead. AVG has installed itself to check Outlook and I can't find any setting to change it. I don't want to uninstall Outlook as one of them may want to use it in due course.
Anybody able to help on that?

I've had a few problems where update wouldn't happen automatically.  It seems to have corrected itself in the past week and working normally (fingers crossed).

No further problems with updates here.
Did another 8.5 install today. Solution to my query above is to pick Advanced Installation not Standard installation.