I can upload images to an entry via the EE File Upload Tool, but not Mark’s File Extension (Win Server) ...wierd!

Like the title says! I thought it was a folder permissions issue on the Windows server, but I can upload files to the same folder using the built in EE functionality without a problem.

Any reason that Mark’s File extension wouldn’t be able to upload an image when EE can?

Moderator’s note: moved to “Extensions: Tech Support”