Hello Tom, thanks again for your help. We found the solution for the problem and actually it was neither a DNS problem nor a problem with ISA/AD. It was just the used version of the IE. According to Microsoft Support it does not with any version of IE prior to IE 5.5 with SP1 (I never thought to blame the browser :-)). See the correspondig request in Microsoft's Support-DB: http://support/microsoft.com/default.aspx?scid=kb;en-us;289858 Regards, Lothar