I understand you have a partnership, but are you officially REGISTERED as a Partnership with the Tax Authorities et al, as well as with Ebay for the purposes of conducting business?

Before Managed Payments, were you running an individual account, or an official Partnership account?

I have no idea what the solution is, but customer service will be unable to assist you. Their talk of the "technical team" is smoke and mirrors as this has been an issue since the new system rolled out more than a year ago.