“What do I do when I get the error message when trying to post a payment to an Invoice: Process Aborted! Current client already in payment application mode or invoice posting/unposting process?”
Go into AR Manager, click the New button, enter the date and the Client-Matter Number, and then hit return. Next, click on Tools and then Unlock Client. Finally, clear the AR record you have open and go back in and re-enter the payment like normal.