Dodgy Webmail

Hi Ya All, we run w2k exchange server on w2k advan server, some users have outlook,but the biggest percentage use webmail. When some users (5 or 6) open there webmail thay can view and read it but if thay try to reply or forward the mail to another user it opens a blank message with only the origanal sender and recipeant/ time and date box in it and no other txt, i have been through the usual properties and settings etc but still to no avail. anyone have any ideas ? thanks in advance.