ipn_main_handler "WARNING: An Error occurred, please refresh the page and try again."

[MeltDown]

Site in question is: beadedlily.com
I've recently upgraded to v. 1.5.1, and am using Paypal Express Checkout. Today I noticed that when clicking on the "Checkout with Paypal" button, I receive the following error:

WARNING: An Error occurred, please refresh the page and try again.

The page this is occurring on is ipn_main_handler.php?type=ec.

I've gone through the checklist on the Zen Cart troubleshooting page recommended by Dr. Byte for this error message but those recommendations do not seem to apply. Plus there are no related error messages in my logs.

Thing is, I don't believe that this error occurred initially, after upgrading. I seem to remember confirming that Paypal was in order, although I could be mistaken.

Any idea what could be the culprit? Thanks!

[MeltDown]

It looks like I've tracked this down: It seems that the Reward Points add-on was creating an issue of some kind. After removing it, Paypal Express is back in order :)