website displays on preview but not client

I have a website which takes JPEG files from a folder on our server and displays them. This way staff can update their own folders with new images and the get automatically displayed on the client.

I am having issues though because all the images display correctly on the design part of the XIBO website and it will display correctly on the preview template view but random (no pattern in file name, size, date added etc and even photos which have displayed before) will not show up and I get a broken link icon. The photos that are not displayed change all the time as well. The photos also display properly on the website if you browse to it.

I have tried changing the type of file and I have the IE7 emulator setup in the registry. Do you have any other ideas what might be happening?