my trial period with avast has recently expired and i have chosen to try another service. but when i tried to uninstall avast pro antivirus i was unable to do so and recieved the following message:
avast!
A setiface error has occured: 536870929
try to reinstall or contact support, please
i do not want to continue with avast and would like it removed from my computer but i dont know how to do so. any help would be great because i can’t try another antivirus product until it is removed.
It would help others help you if you noted which OS you’re using and which version of avast! Pro. 
In the meantime see topic below and read the 2nd post by Tech (Items 1 - 4):
http://forum.avast.com/index.php?topic=56904.0
You might try turning off the self-defense module. Not sure where it is in Pro. In avast! Free it’s: Settings>Troubleshooting.
If your operating system uses User Account Control, turn it off and then try to uninstall. I’ve been able to uninstall some programs that wouldn’t uninstall otherwise by doing that.
Beyond that I don’t know.
I think the uninstall tool will do the trick.