SB v4: Error 75

I am running Windows XP Home with SP2. ZoneAlarm Firewall & Antispyware, AVG Antispyware and Avast antivirus.

Previous version of SB worked fine, updated to v4 and it works fine except I get the following error message when SB tries to automatically update when I first logon to a limited profile or when I try to update manually from a limited profile.

ERROR DOWNLOADING FILE

Cannot write file to disk
Error 75: Path/file access error.

There is no problem when updating from a profile with administrator status. I have tried altering the permissions in the registry but without any effect. Any ideas?