Blackthorne is eBay's auction management software; it's used by volume sellers, including one of my customers. Version 3.1.40.0 was released 1/30/07 and my customer was distressed to find that unlike prior versions, this version would not run on a limited user account. The necessary hack is on the attached pdf. I've also sent it to Blackthorne's tech support. I debugged this with Aaron Margosis's LUA BugLight, which turns out to be a fabulously good tool -- much faster than using regmon/filemon because fewer irrelevant Access Denies are reported.
The vendor responded with an alternative here:
HOWTO__Running_eBay_Blackthorne_on_a_Windows_Limited_User_Account.htm