input field does not get the focus

Hi all,

I've a strange problem. We use Internet Explorer 6.0 and a program which is
written in ASP.NET to do our business. But many users cannot input into input
fields or change the contents in them, because, if the user click an input
field with the mouse, the input field does not get the focus. These fields
are all on popup windows. But I can do it without problem. So the programm
must be OK. I think that this problem is caused by settings of IE. Do you
have an idea which setting will cause this problem and how should the setting
be changed to solve this problem? Many thanks in advance!

--
Weichao Wang