It may have to do with your Client Access configuration. Check to see if both the check boxes for avoid duplicate names are check. They should be in most cases.
Also check to see if a workstation ID was entered or the use WIndows user name radio button is ticked. I have not had any issues with the screen size causing log in issues. I do have it set to 27×132 for reading spoolf iles without having to window left/right.