Editor does not display in IE

Fck version 2.4.3 has been working in our system for several months. However, we just had several users complain that they could not see the editor when using IE. It works for me (IE6 and/or IE7) - however, other users in Australia are saying that it is blank on the page where the editor is supposed to display? Could it be settings in IE causing this or is there something I could look for in our install. We are using ColdFusion.

thanks