Problems uninstalling Quartus in Windows XP

When I try to uninstall Quartus II 9.1sp2 using the Tab "Uninstall, Repair, modify" ,I get to the Install Shield which tries to re-install. As there is already an installed version, it ask to uninstall. I click and then I get a Pop-UP

"Another instance of this setup is already running. Please wait for the other instance to finish and then try again"

Note I've rebooted my computer and it didn't help