Can't boot Windows XP Embedded

I have a 'diskless' workstation that is running Windows XP Embedded that seems to boot OK but when it gets to the point of logging in, it gives the following error:
"Windows cannot create a temporary profile directory."

Clicking "OK" at that point takes me to "Logging off ..." where it hangs.

I suspect the flash card that's configured as C: is full and that's what's causing the problem. Problem is I can't get booted via some other method to clean it up. I've tried booting Safe Mode - that goes through the list of drivers as it loads them, gets to the last one (Mup.sys) and hangs there. I tried hooking up a CD drive and booting from a Windows install CD - that gets to the point of "Starting Windows ..." and hangs.

Any other ideas on how to get this thing booted ?!?

 

Thanks, plodr, for the suggestion. So I cracked the case, got the card out, installed it in my desktop and it turns out it's not full. There must be something wrong with the user profile that it's autologging on with that's causing the error. There are 4 other users, though. So the question is:

1) How can I get out of the autologon to try the other users to see if one of them will work?

2) I found a Microsoft KB article that shows how to enable/disable autologon but it involves editing the registry. If I install the card on my desktop, how can I edit the registry on that card rather than the one on my desktop's HD?

 

Thanks again, plodr, for trying to help.

The KB article is this one: http://support.microsoft.com/kb/315231

Other things I've tried:

1) In looking at other posts here at MG, it seems like I should be able to get to a logon by either holding down the shift key while Windows boots or by Ctrl-Alt-Del once it's booted but neither of those seems to have any effect. Could this be due to the ForceAutoLogon registry key?

2) With the workstation's flash drive on my desktop as E:, I've tried setting systemroot to E:\windows and running regedit but I get "The application failed to initialize properly (0xc0150004)" from regedit. Is there something else that needs to be done to edit the registry on E:? Is there some other tool I could use to do this?

Any help would be greatly appreciated.