When running XF 1.0, our user upgrades system worked fine...now that we've upgrade to 1.1.0...I'm finding myself having to manually upgrade users. This is NOT cool, and we have a LOT of VIP upgraded users...what is going on?
Those may be old errors, as that should be "Invalid business or receiver_email" now (as 1.1 checks both). Nonetheless, the value you enter for the PayPal account in XenForo should be whatever PayPal is sending through as the "business" value.
If you're sure that's correct, then submit a ticket and we'll see what we can do to debug it.