Quickbooks Desktop Sync Error - "There was an error when saving a Bill. QuickBooks error message: Only one a/r or a/p account allowed per transaction."

Cause

You have an AP Account or AR Account coded to a GL Account line item in Beanworks. 

Resolution
You'll need to reset the invoice and remove the account. It's not possible to import an invoice into QB with an AP account coded at the header level and AP/AR account also coded at the line item level.