If you still can boot the VM do this:
1. power off VM completely
2.add second vmdk - same size or slightly larger than the existing one
3. boot VM into your favorite Linux LiveCD
4. clone disk to disk with ddrescue - like
ddrescue /dev/sda /dev/sdb /tmp/clone.log
5. when that is done replace existing snapshot-chain with the newly created vmdk
6.done

Ulli