Many thanks for the swift replies, much appreciated.
It is a 1GB HiMD disc that I was using. I had been using it all day and for the previous two years without any problems at all. Since that happened I have tried using other discs, just standard MD discs without any problems at all, both reading and writing. (I only have 1 HiMD disc)
I have tried the damaged disc since I did this and the same problem occurs unfortunately - It can't read the disc, listing the same 'format disc error', depsite other discs working fine.
Any suggestions as to how to get it to work, or anywhere I can get it repaired? I contacted Sony US but they do not offer a repair service for MD any more :-(
Thanks
James