Hi, I know this may be a bit late... but I had the same problem on my SC-HT540.
As a last resort I decided to try to update the firmware on my player but I couldn't find out which "System Controller" I had (due to the "ST Mode"). I decided to guess it was the "90B", (the same as a HT535), as I had read you could not install the wrong firmware.
I got the latest firmware from here: http://www.dcevolution.net/panasonic/index.php?option=com_content&task=view&id=78&Itemid=113
When I tried to update the firmware it reset the player and then told me the upgrade was complete. The player then worked fine. I could check the firmware, region and system controller info, and in fact discovered I had a "100B" controller, so no upgrade had happened.
I hope this will help someone else, and prevent them shelling out for a remote to restore their player.
P.S. The region free hack we had been trying to introduce when the problem occured now works!
Taz Tasman
May 2007