Have you checked if the LT-icon in the toolbar is not a ‘ghost’?
one of the macs at work had this issue with a network monitoring agent: the program-proper had been removed by a bogus (we learned later) cleanup tool, but the file that created the top-bar icon was still there and caused both installer and uninstaller to fail. (installer said “program already installed” while uninstaller said “no such program installed”)