10413 error when using "Check out with PayPal" button

So we got an e-mail from a shopper who was getting this error when checking out. After some back and forth communication, I asked them to tell me EXACTLY what they did so I could figure out why she had an issue that NO OTHER customer had reported having.. I have NOT been able to replicate the problem..

Here's the e-mail the customer sent describing the problem they had..

------ Forwarded Message
**From: **ac t ****_**[email protected]
**Date: **Sat, 6 Sep 2008 15:52:39 -0400
**To: **Phlaunt Hair LLC [email protected]
**Subject: **RE: Order Update #26

Thanks for following up. The steps that I took both before and after logging in and was unsuccessful each time:
Went to Phlaunt shop.
Clicked phull lace wigs icon
Lead to page that lists all units available
selected 1 curl, 1 malaysian
add selected items to cart
selected checkout with paypal
logged onto paypal
selected payment method
confirm order
after selecting confirm order, this is where the error message kept coming up
I went again through the paypal process, came full circle and still kept getting the error message (even after verifying the number of units (1) in each category that I wished to order.

At that point, I logged out. Logged back in, went to my cart and saw 1 of each unit still in my cart with the 1075 total. I emptied the cart and tried the above steps again and the order would not go through due to the same error message. I could not figure out what was mismatched. So I emptied again and just bought one at a time. Hope this helps.What she did differently than other customers was to use the "Check out with PayPal" button. This is the ONLY customer who's gotten this error..

Here are some of my store settings:

Order Totals Settings
Action ****/ Sort Order
COD Fee - ot_cod_fee
Discount Coupon - ot_coupon - 280
Group Discount - ot_group_pricing -290
Gift Certificates - ot_gv - 840
Low Order Fee - ot_loworderfee - 400
Shipping - ot_shipping - 200
Sub-Total - ot_subtotal - 100
Tax - ot_tax - 300
Total - ot_total - 999

          My Store Settings
      **Title                                    ****/ Value**
      Display Prices   with Tax  - false  
      Display Prices   with Tax in Admin - false 
      Basis of Product   Tax - Store 
      Basis of Shipping   Tax - StoreNow after reading some of the posts here regarding this error, I made changes to the store settings highlighted above. I changed the values from "Shipping" to "Store". Is it possible that this change should resolve this issue?? Is there anything else should I be checking/modifying?