All of a sudden, my client is screaming that customers cannot complete transactions because they are getting an error when they are sent to the PayPal page:

"Sorry — your last action could not be completed"

This occurs when they click the PayPal Express Button. In IE8, if they complete the checkout process, but still pay through PayPal, it works fine. In Safari, PayPal does not work at all. In FF, everything works. IE8 in compatability mode is working fine as well.

Debug logs don't seem to be telling me anything useful.

Any ideas here?

btw, same goes for the other PayPal IPN module.