I'm having some login problems on my laptop (WinXP Pro SP2). The exact phenomenon varies. E.g. when I try to Switch User, it declares some parsing error in line 903, and after 10 clicks on "Ok" it returns to the original user (i.e. doesn't switch). Logging out altogether (from the first account) gets rid of this particular phenomenon. Alternatively, from the login screen, some of the users are inaccessible. Clicking on them and typing the password results in a return to the login screen.