I have received this error in MSP07 frequently and occasionally in MSP10- every time it has meant a corrupt file, and non recoverable. I don tknow abotu 13, but I would assume similar (not good news, but havent found anything that gives hope yet).
every time I have reverted to a backup- I tend to save at LEAST every hour, or any time that I make any mods of a significant nature. Hoping you have a backup or 20 you can revert to- if the worst comes to the worst, take it as an unfortunate lesson. Not good I know, but I found out th ehard way that backups can be inconvenient but they are useful.
Failing that you may have an autosave somewhere, or possibly a shadow copy that you can restore- I have sometimes gotten shadows that load and work fine.