This error is strange in that the user can access the policy file directly, so this appears to be a problem just on startup. I have tried to chase this down but to no avail. The most prevalent reference is to DNS but we have no DNS issues that I can find.
This may be a Registry permissions issue. The reason you may only be seeing the problem once is because it is only being accessed once at startup or login. Search on any keys in the Registry that match the listed GUID and see if they have the proper permissions set on them.
This was first published in December 2003