Do you have a sample URL we could look at? It's hard to diagnose what the
problem could be without seeing the example. Sometimes it's something as
simple as the file extension is incorrect (it's labelled as a .gif, but it's
really a .jpg) or that there's an illegal character in the filename. Even a
space is an illegal character though usually the browser and FP are smart
enough to replace it with %20, which is the URl code for a space.
Hope this helps,
Mark Fitzpatrick
Microsoft MVP - Expression