[Zope] can not put Photo with webdav

Hi there, I am using the Photo product. The Potos have names like Picture.jpg (so they are recognised correctly) Now I like to edit some of the photos trough webdav using DreamWeaver and Fireworks. When I try to chekout a Photo I get an error saying that the operation was denied by the server. With non Photo-images this works fine. Is there something I can do? Or is it just not possible to update Photos trough WebDAV Robert