Haven't seen this one, but if your doent is still open, try copy/pasting the
contents into another FreeHand doent and then saving. Try exporting into an
older version of FreeHand.
If that doesn't work, try copy special/eps and then pasting into Illustrator.
(Then export later)
Last but not least, take a screen shot of your work and trace over it later.
(It beats coming up with it from scratch.)