updates

I am unable to update several of my Mac App Store purchases without first deleting them and then reinstalling. This is a presistant problem that I can't seem to work around. I have trashed the pref files, and cleaned all the caches but I still have the problem. I keep getting the message to sign in with the account that I used to pruchase the App. I only have one account and when I delete the App and reinstall it the account is accepted. I even contacted the Apple Techs and they were useless. At one time the App Store kept prompting me to upgrade angry birds. The problem is that I never pruchased it. Is this my problem or is the App Store not ready for prime time?