I've look around the net but can't find anything on this odd problem. When in Preview, if I open the the Help menu I am immediately presented with a username and password dialog for my iDisk. If I enter them my iDisk mounts just fine and help opens. If I cancel, help opens too.
I've reset the Help system, deleted all help plists, etc. to no avail. It only does this in Preview and only in one user account. Any ideas?