I also get the message "not enough user rights to continue." I am already logged in as administrator on this, my home computer (a Win2K system)
I seem to recall I had difficulties on the last program update too; checking email archives, I had to use a special uninstall tool from Avast before I could finish the job. That was after cleaning the registry, trying to install in safe mode, etc. I hope I don't have to go through all that again! I sent an email yesterday about this problem, hope to get an answer early this week.