There is another and very complete troubleshooting guide:
http://www.pocketpcfaq.com/faqs/acti...shoot-as4x.htm
The 8503001 error is listed in the appropriate section, but a quick scan of the text for that error did not look promising ... I hope there is something on this site that can help you.
There is also listed an 8503000c error, which looks like it may give you a clue ...