Stuck in logon/logoff loop

I have created an embedded build that works great on a disk with a single
partition. I am trying to migrate this build to a disk that has multiple
partitions and am using ntldr to load the partition with XPe.

It boots up as I would expect but when I get to the logon screen and logon,
it immediately logs me back out. I edited the registry offline and added
administrator auto login, and that just put me in an infinite logon/logoff
loop.

i have replaced explorer as the shell with my own shell. The value of the
following registry key by default is:
"SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit REG_SZ
"C:\WINDOWS\FBA\FBA.EXE -run

I tried changing that to "C:\windows\system32\userinit.exe," without any
luck. I'm at a loss. Does anyone have any suggestions at to what the cause
of this problem is?