Holger thanks for your answer.
I just checked both folders:
images and downloads
In both there is no file called index.htm (no htm there @ all).
Images just contains image/flags (sub folder)
and in the image folder there are only jpg and gif files
The download folder contains a mix off zip and pdf files
I checked the server settings with my hosting provider.
Save mode is off
and there is a check box for register global activated, I checked that to be on.
I tried both options though, so save mode has been on and register global has been off.
Nothing seems to be the trick.
The entire site has been copied to another domain, there it seems to work just fine so there must be something with the server settings.
My domain provider is one of the biggest in the Netherlands so I don't think they have options missing that should be there..
This is starting to do my head in now..
next try is erasing the entire site from the hosting server and start all over with a clean install (no templates, plug-ins or what ever).