Can’t run 16bit programs error

Had a new XP install with SP1 integrated and I changed a key in HKEY_LOCAL_MACHINE – SYSTEM – CURRENTCONTROLSET – CONTROL – FILESYSTEM NtfsDisable8dot3NameCreation from standard 0 to 1 effectively disabling 16bit apps to run, thinking they would not need this and thereby improving performance. Woops, they need a 16bit app to install, so I changed the key back to 0, but it hasn’t made any difference. Rebooted loads of times, PC been switched off over weekend, actually recreated that key but still get error.
Just ran SP1 again but made no difference.
Anyone got any ideas please??