Hi Rick,
Thanks for your answer, the user who had those request problems is a normal Windows user with a ADSL modemline. So there's no search engine involved. It's the first page the user request, so this is the /forum/index.php or the follow up page, but the user gets a empty screen, no images are shown or any text.
Maybe this is some usefull information? I'm willing to turn off the HTTP referrer but this server i'm talking about is not under my management.... So i can't make any changes to the server here. This is at my ISP.
Rob
