Gridmarket in Multisite installation: Products of users shop not visible on main shop site

Hi,
I have a Multisite installation and marketpress installed. I created a users shop and added a product to his shop. I have also two products in the main shop. The product of the user is only visible in the users shop, not in the main shop.
I configurted the theme to view global products. The strange thing is also that I added the categories widget and I can see that there is a product in the specific users categorie - but when I click on the categorie it says "no product". I do have also "TT Marketpress Frontend Admin" and "New Blog Templates" running if this is a useful info. At the moment I don't have an idea where I can look into to solve this. I hope you guys can help me.
Thanks,
Marc