1. You say you're getting the ot_tax errors.
2. You say you've installed the patch (which fixes those errors when applied properly).
3. You say you can "purchase using credit card through PayPal". How exactly is this different from the error you were reporting earlier? The more details the better.
4. In addition, I suggest you turn on debug logging, and post your logs.
http://www.zen-cart.com/forum/showthread.php?t=61199



