Fatal error: Call to a member function on a non-object in

Ok so I am suddenly getting this message now. the only thing I had been editing was the stylesheet for my template which of course I tried backing out. Strangely if I wait a few minutes I can seem to get to the homepage of the cart which is /storefront but then upon the next click back it comes

Full error
Fatal error: Call to a member function on a non-object in /home/saltycri/public_html/storefront/includes/classes/category_tree.php on line 68

Line 68 is
$categories->MoveNext();

And if I pull up lines 65-72 of that page it shows

if (!isset($first_element)) {
$first_element = $categories->fields['categories_id'];
}
$categories->MoveNext();
}
if (zen_not_null($cPath)) {
$new_path = '';
reset($cPath_array);

any ideas what happened? store address https://www.saltycritter.com/storefront

Had you done anything within 2-15 minutes prior to changing the stylesheet on your shop?

Few things I had been toying with but not sure if it was within 15 minutes such as I changed one of the product types name and edited one of the attributes along with created a pruduct option from the cataglong list in the admin but I think that was longer before on each account.

The change on the product type ... can you expand on that?

I edited the 3rd product type which I think was called Document - General maybe to Snails and Crabs by editing the Product Type name. And looking further after you asked the above question I noticed that I must have somehow made the drop down called a SubType the same catagory... Even though I dont really yet understand this whole product type thing yet as was playing with it in atempt to solve my other question here http://www.zen-cart.com/forum/showthread.php?t=35345 it dawned on me that having something be a subtype of itself would be a conflict or a potential one at least. I changed the drop down to make it a sub cat of Products General and the error has gone

Document General is a special Product Type that is not designed for selling and lacks in most all of the features needed for a Product ...