[Zope] Edit Subclass of File using ExternalEditor fails

Hi, I have a ZCLass with File as the base. I need the possebility to edit Instances of this class with ExternalEditor (0.7). Opening the Editor works fine, but when I try to save the file back to the server it claims Error occured during HTTP put: 405 Method not allowed I have all permissions to "777" - it can't be something with permissions - or ? Any subbestions? regards Harald