How can I open the disc tray on Panasonic DMR-EH50?

I have just put in a RW disc to my Panasonic DMR-EH50, to copy stuff onto and it is now stuck in the tray - the tray itself won't open and the whole recorder freezes when the eject button is pressed. You can hold down the power button on the unit to turn it off - it then comes back & spends several minutes performaing a "self-check" before coming back OK. I can then get into the hard drive content ok, but still same prob with the disc. Anyone know a way of forcing the disc tray open, so I can at least get the disc out?