In my experience, this type of thing is usually caused by a field being blank that is used by the system to trigger the form.  I would go back through the depreciation screen and make sure you have all the fields filled out.  

For instance, the same thing happens in charitable donations if you don't have the description field filled out.

If you go through all the fields and can't find one that is blank or filled out incorrectly, then call the helpdesk and they can tell you which fields trigger the form.