That's weird, but it could be the cause of your problem. Please have a look in
Code:
HKEY_USERS\.DEFAULT\ControlPanel\Desktop
for the same entry. Also, please double check that it really doesn't exist in the first location. If you're sure it doesn't exist in either location, create a new entry in both locations, type should be string (the type that has the "ab"- icon- sorry, I'm on a german version of Windows here), and set it to the default value of 5000. Reboot and retry.
I probably don't have to tell you that if you muck around in your registry, Bad Things could conceivably happen, right? So please, be careful.