Upgrade Oscommerce to Zen

I'm having a problem upgrading Oscommerce to Zencart.
All of the products are in but allot do not show on the front of the site or in the admin. Searching for product model codes for the missing poducts yields no results.

I know they are there because if I try to copy an attribute from a product I can see I can see missing products in the product to add attributes to dropdown.

The store admin and front end report 1144 products which is correct but on the Oscommerce shop there are no empty categories and on the new site there are at least 6.

I'm not sure what the problem is and relinking master categories from the store manager does not make these products display.

Suggestions please

Thanks

It looks like I have invalid master category id's
I found this by using the brilliant quick updates mod

How can I assign these invalid products to their correct category ?

Thanks

I've edited by hand the master_category_id in the product table where it was 0 it is now 194 which is category id number of a new category.

Products_to_categories does not have any 0's in it

It didn't work though and I still have around 200 products that are set to an invalid master category. I have looked at the product-to-categories page in the shops admin but this does not look like it does what I want as the product must have a master category id before it can be linked to other categories.

I'm desperate

Can someone help me or point me in the right direction

Thanks