Error opening file - Code 149, bad data offset

Hello. I was working on a multitrack project this morning, saved - went to lunch and repoened to finf the .sesx file won't open. 

The error message is "Error. This file is not supported by libsndfile. Code: 149. Bad data offset"

I cannot find anything online about this error - the original audio files are in tact but for some reason my earliest autosave backup is from about two hours previous before I did all the work. I just need a way to open that file PLEASE help. This is not what I wanted on a Friday afternoon 😞