[Zope] ZClass question

Hi, Something that seems maybe very trivial, but I did'nt find the solution. I have a very simple class ItemId (metatype ItemClass) which is only a subclass of Image and has no property sheet. When I try to create a new instance I get the following message : Error Type: TypeError Error Value: argument file was ommitted Here is my addMethod: ....... <dtml-with "ItemId.createInObjectManager(REQUEST['id'], REQUEST)"> <dtml-call manage_upload(REQUEST['myimage']) </dtml-with> ...... Where 'myimage' is the name of a field of type file in my input_addForm. I works fine when I use manage_upload with an Image but not when it is a ZClass subclassing an Image. Where am I wrong? Thanks.