I have been getting a rash of failed updates of my virus definitions since 10/21 (which I believe is when I updated the software to .1269). I have tried to manually update and it runs for between 3 and 5 seconds and quits the update process. What can I do to fix this?
Avast main GUI → settings → updates → no proxy (direct connection).
Then save settings and reboot.
Please report back.
Have you tried a repair? It’s easy and painless.
Control Panel…click add/remove(XP) or uninstall(Vista and Win7)…double click avast…scroll to and click “repair”…reboot. Hope this helps. 
I attempted both these fixes, the first did not work and I found that I can’t open the uninstall/repair window for avast… I can open it for other programs though. Any new suggestions or theories as to what the heck is going on?
Then it looks like your installation is corrupt.
This assumes you are using avast free:
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Download the latest version of avast, 6.0.1289 http://files.avast.com/iavs5x/setup_av_free.exe and save it to your HDD, somewhere you can find it again (if you didn’t save your last download). Use that when you reinstall.
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Download the avast! Uninstall Utility, aswClear.exe find it here and save it to your HDD (it has uninstall tools for both 5.x and 6.0.x).
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- Now uninstall avast! (using add remove programs, if you can’t do that as appears to be the case for you, start from the next step), reboot.- 2. run the avast! Uninstall Utility from safe mode, first for 5.x if previously installed and then for 6.0, once complete reboot into normal mode.- 3. install the latest version, reboot.