Cannot help directly. I have a 9Mb Quicken file which I back up to 100 Mb Zip drive (rotating discs for each save) with no problems. So you should have no problems putting it on a 3Gb drive.
However it may be worth doing an error check (scan disc) on your D Drive which may have developed a number of bad sectors and could be on the way out.
Can you save other files to the D drive?
ps for really important files I never back up to any internal discs.