[Zope] ZClass Product Difficulties

I'm having some difficulty with using my ZClass as a Product My Product works fine as I have built it, inside Zope - I can create new 'MyProducts' fine from the "Available Object" dropdown. I then create a distribution with the Control Panel distribution tab. Then I remove my development version of the product, stop Zope, untar the distribution product .tgz in the right place, and restart Zope. MyProduct appears in the Products list OK, but it doesn't appear in the "Available Objects" drop-down, so I can't create one anywhere. I'm going mad trying to solve this so any help would be appreciated! Thanks -- Edd