My XP now logs me out when I log in ??

Installed Vista Beta 2 to my 2nd SCSI drive
Made it the 2nd boot option after the CD

When I now revert back to the first SCSI being the 2nd boot (for XP),
the system boots.
When I login it then automatically logs me out, regardless of the account
used (incl administrator).
Safe modes solve nothing; still get login dialog.

I note while it logs in the background image is missing but the desktop
color is correct.
Also whilst XP booted to the list XP accounts rather than the login dialog,
it now boots to the login dialog.
------
It continues to log me out if if I retry.