What are the account requirements for sellers in marketpress

MU with BP.

I have a seller on my network who seems to be unable to process payments via paypal. I'm using chained payments. When a live transaction is attempted, it errors out on the very last step and PayPal returns "This transaction cannot be processed". It does not return an error code.

All other sellers are having no trouble processing transactions.

I've done a bunch of troubleshooting already. Changed themes, deactivated plugins. I've gone over her marketpress settings with a fine tooth comb. I even went so far as to input my own PayPal account info into her website and was able successfully complete a live transaction. When I put her PayPal account info back into her website, the transaction failed as before.

She has already called PayPal once and they told her that her account looked fine. I know she can send and receive money otherwise.

The question is, what are the requirements and settings, if any, for a PayPal account to work as a sellers account with MarketPress? She is using an unlimited, verified, business account. I know there are dozens of settings in PayPal account profiles, is there anything specific that she should look to to make it compatible with MarketPress?