User Interface Failure - Logon User Interface Dll Msgina.dll Failed To Load

Current situation: When Windows XP boots it displays Windows logo, black screen and then a small error window with title "User Interface Failure" and text "The logon user interface dll msgina.dll failed to load. Contact your system administrator ..." There is a button to restart the system. Booting causes a loop back to the same state; I cannot get the system to boot to safe mode. Other than the lack of a logon and desktop the rest of the boot process seems to continue OK; I can access network shared drives from another system. Using BartPE I can see that msgina.dll is in C:windowssystem32 as it should be. Unfortunately much of the data I need to access for my work is not on shared drives and cannot be accessed by BartPE so I am in big trouble.
Background: The express version of SpyCatcher was installed a few daus ago. All was OK until I restarted the system and arrived at the current situation. I also have BartPE which I have used to look at the SpyCatcher logs and found entries that msgina.dll was quarantined (along with many other safe items). I believe this is the cause of the problem and not anything else.