Mine and daughters computers, no problem, wifes had a problem with updating a priority update today so i checked and found the virus database was dated 18th June. Tried updating it but it wouldnt so just done a uninstall and then reinstalled with latest (todays) edition and everything now fine.
Recommend that you check the date of your virus database
I have noticed it tries to download updates as the computer comes on, i realise this is because AVG is one of the first programs to load up ( anyone that had AVG on win98 will have noticed this because AVG does a boot sector check as the computer starts, this is not shown with XP and Vista because of the start up screen )and if it's set for automatic updates it tries to do so as soon as it starts, this does cause a problem because connection to the net is usually one of the last things to load.
Should i get this happening, i just wait till the computer has fully finished starting, then double click on the AVG control icon in the task bar and manually check for up-dates.
Have you got a firewall blocking access. Check when last succesful update was carried out. If you haven't received one since it could be your firewall.
You are on XP2 aren't you?
It could also be a large update. depends what you mean by large update.
If the scan is taking a long time you may be scanning everything and that might need some tweaking.
I personally don't run anti-virus software because they cause more problems I think. I use anti spyware/adware stuff because the biggest threat I believe is from Iexplorer highjacking.
I run XP2 with the firewall, that stops most stuff. I haven't had issues for a while but I do tend to stay away from amature sites and don't run any peer to peer software or messenger.
I look after the infrastructure for a small building society (thought thats about to change!). We run Sophos but I rekon we detect less than a virus a month and normally they are harmless. We do have web filtering stuff as well but we check for viruses first and they are few and far between.