I had a similar problem recently, I had a response from "Lastchip" that cured it for me:
OK, try this but be careful.
I, like our Forum Editor, am reluctant to post Registry Hacks, because they can go wrong - Big Time, but sometimes, it is the only way to overcome a problem. So please read this with care and follow the instructions precisely.
CAUTION: DO NOT CHANGE ANY SETTINGS EXCEPT AS INSTRUCTED.
On your XP MACHINE:
First: Go to Start; Run; and type; regedit [OK]
and look for a DWORD restrictanonymous and see what the value is. If it is anything but 0 (zero), close regedit to follow the next part of this post. If it IS SET to 0, this post no longer applies and it isn't the root cause of your problem.
Next, go to System Restore and make a backup of your system, in case things go wrong.
Now, reopen regedit and as a further backup, go to Registry (top left) Export Registry and save a copy of your registry to the root drive (C:). This is a further safety net should the need arise. I don't wish to frighten you and with this hack, things shouldn't be a problem, but you can't be too cautious when dealing with the registry.
Finally, navigate back to restrictanonymous (as above) RIGHT CLICK the DWORD, select MODIFY and change the decimal value to 0 (zero).
A further word of warning, there is a DWORD restictanonymoussam just below the one you want - DO NOT change this.
Now close regedit and reboot your computer with your fingers and toes crossed ;-) and all should be well.