cannot assign any categories to products

Following the documentation help for adding a product to a category does not help. In all browsers tried (Chrome and FireFox) on JOOMLA 3.0, when click the ADD button for the category within the product edit page in the backend of Joomla/hikashop, instead of getting a popup, I am redirected to the "administrator/index.php?option=com_hikashop&ctrl=product" products listing page again.

In fact, no matter which ADD button I click in the product editor form, I am redirected out of the form and back to the product list page. I use no popup blockers, and have no problem with modal windows.

The default "product category" is assigned when I add products and there is no way to add my subcategory to a product.

This is on a GoDaddy hosted server.

Thanks so much. I will try again.