Hi! Thank you for replying to this.
I am not sure where my last backup was from, but my wallet was still accessible from 0.9.2 in Windows the last time I remembered, with the same password. So probably the client updated with the live wallet data which still worked but the backup has no longer been compatible.
However, I just tried exporting from 0.9.2 again and loading that JSON export into 0.9.3c and again, I'm greeted with the same error message...
Will try logging in from 0.9.2 again with the same password and see if I have lost my funds for good. Hopefully this is only a 0.9.3c thing, but looking at the lack of complaints on the board, it doesn't seem so.
Once again, thank you for your reply.