Categories not Displaying

[green_bean]

I have recently imported products and categories into a fresh 1.6 install using a csv file.

 

The categories are displayed in the back office (in catalogue>>categories), but do not seem to be linking with products or being output the the front of the site.  When editing a category, there is nothing listed in the navigation tree except the root, "home"

 

In the product associations, only the default category set in the previous installation is displayed.  Clicking on the drop-down shows no other options.  Only the home category is listed in the navigation tree, it expands, but there are no categories listed.

 

Categories are listed in the "Top Horizontal Navigation" menu, and the menu items display when I manually add them.  However, they all link to the root of the website.

 

Is this a common problem, and are there any suggestions as to what I should do?

 

Thanks for the support.