Warning when canceling a window

I get an warning when I cancel or escape a window. After canceling and the thickbox disappears, click on any link and you get an error

User: Guest
Place: http://siteurl.com/ajax_register/login&random=1262006298138

Message: call_user_func_array() [<a href='function.call-user-func-array'>function.call-user-func-array</a>]: First argument is expected to be a valid callback, 'user_pass' was given in C:\PROJECT\includes\form.inc on line 372.

Please help!