[Flubflow]

HINT: When you've downloaded and run the AVG setup it may ask you if you want to Repair Installation or uninstall. I tried repair and it still didn't work so choose uninstall. When it asks to remove your old settings then do so. When uninstalled, remove any files that may be left over in the program files\grisoft\avg directory. Also remove any avg related program entries in your firewall (you can add new entries after install as and when required)
Reboot then run the setup again and install as normal.

That took care of the "update was unsuccesful" instant error - not to be confused with other errors such as time-outs, connection/firewall problems etc.