I have seen this before, and I believe it to be a bug in the Admin which masks the problem. Even if products.products_quantity_order_units is 0, it is displayed as 1 in the Admin during product edit.
Looking at admin/includes/modules/product/collect_info.php, line 378, if $pInfo->products_quantity_order_units == 0, 1 is displayed. This is misleading.
Geezer, to fix your problem:
- On the product info page, you will see (in the Add to Cart box) "Add to Cart: 1" with "Units: 0" below it. This is the trigger that you're in this state that Ajeh and Kobra are describing.
- You go to the admin for this product, and see that Product Qty Units is 1. It's really 0. Just go ahead anyway and update the product. The 0 will be overwritten with 1.
- Go back to the catalog product info page, refresh the page, and the Units: 0 should be gone.
Good luck,
Scott