HELP!  I've been a QuickBooks and QuickBooks POS user for over ten years (several versions of both).

I use the RDS Server to connect my POS computer (QuickBooks POS v12 r19) to my back office computer (QuickBooks Desktop Pro 2018). All has been fine until this afternoon.  My back office computer is getting an "Application with Revoked Certificate" message ("revoked by its certification authority") and will not start.  How can I correct this???