I once had this exact same problem years ago. At least in my case i found the uninstaller data had been deleted from the registry. Look for HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall
For my case, it also happened on a disk drive i had just imaged so i was able to recreate the problem and able to recreate the problem at will to determine with 100% what was the cause!! It happened when I uninstalled Yahoo Browser Services. Intereseting that when i posted what i found, someone replied about 2 weeks later they had same problem and had just uninstalled yahoo.
any chance you chanced uninstalled yahoo?? would be interesting if years later they repeated the same bug