New Error When Trying to Add Products to Cart

I am getting this error when I try to add any of the products to the shopping cart with the rest of the screen blank. Then the bottom half of my right hand column shows the error when I push the back button

1054 Unknown column 'products_sell_quantity' in 'field list'
in:
[select products_id,products_sell_quantity,products_less_quantity,products_coupon from zen_products order by products_id]

I was trying to install a new add-on but couldn't get it to work so I tried to delete all of the files associated with it and deleted the wrong thing so I copied my files from my backup.

I think I have ironed out the bugs except for this main one.

Appreciate any help or suggestions.
:blink:

One or more of your PHP files is still looking for things the addon expects to find in the system. You'll need to find the offending or altered file and fix it.
One approach to that is this: http://www.zen-cart.com/wiki/index.php/Troubleshoot_-_Diagnosing_Obscure_Issues