To fix an invalid date error in 8.6 launch RPRO from the MAIN or license server, click the “Retail Pro” button in the corner until you see the change current date button, click “Change Current Date”, change date back a month and click “OK” when prompt appears. Click “Change Current Date” again and change the date back to the current date and click “OK” when prompted. Close Retail Pro and then relaunch and log back in. The error should not appear any more. If its V8.52 follow the same process from the computer with the key.