Corel Draw : Error Reading file problem

I have a number of files that I can not open in corel draw.
These were created a few years ago using Corel draw 7.0 on a PC running Win95 or 98.
I have re-loaded CDR7 on my current PC running Windows2000 and I get the error "Error Reading /..../xxx.cdr file"
On the most critical file, the progress bar at the bottom gets to 40% before the error message appears.
I can load and save new files without problem, but some (but not all) of the old files are unreadable.
I have found an old hard disk and installed Windows98 and cdr on it - no effect.
Also I have installed the printer driver for the printer that (I think) was used then - no effect.
Any suggestions ?