We are unable to reinstall Task Server on a Site Server that had previously been a Task Server. There are reminents left behind from the previous install that were not cleaned up properly.
Log Name: Application
The previous uninstall did not clean everything out of the registry referencing the previous install of Task Server.
In the registry search for Task Server under "HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Products". Find the key/s, export them (just in case) then delete the key. After you delete all the keys run the installer again and it should complete successfully.
SMP 7.5 SP1 HotFix5