Never heard of Revo uninstaller but just looked it up on the web.
Trouble is, because you did not use Windows to uninstall AVG then Windows still thinks it is installed and so reports you have two AV programs installed.
Only suggestion I can think of is to reinstall AVG and then uninstall it the proper way, through "Add and Remove Programs".
Why do you use a program like Revo when Windows provides a uninstall process?, I cant see it gains you anything, and in this case loses you a lot.