>>>The page then displayes properly.
>>>
>>>Do you know what may be the problem?
>>
>>Does the form have a javascript WebForm_DoPostBackWithOptions() method?
>
>I assume it does. How exactly can I tell or test? I believe it's a master page for the website.
>
>BTW, if I try a different login/password combination (I just tried), the page works just fine and doesn't give me the same error.
>
>May I please give you an exact URL in private so you can see for yourself?

Sure. But pls include examples of login data that work and that do not.
Also it's end of play here for today so I won't get to look at it for a few hours....
Best,
Viv