No files attached, just a simple mod to make so your code doesn't break when deleting empty categories:

Edit /admin/includes/general.php
Change the lines:
//++++ QT Pro: Begin Changed code JOC
qtpro_doctor_amputate_all_from_product($product_id );
//++++ QT Pro: End Changed code
}

To:
//++++ QT Pro: Begin Changed code JOC
if ($products_id!=null) qtpro_doctor_amputate_all_from_product($product_id );
//++++ QT Pro: End Changed code
}

This stops the qtpro_doctor_amputate_all_from_product function from being called when there are no products under a category.

Pete

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