Greetings @Jamesn190808
Did the engine crash or have a power outage or anything of that nature? Or did you just go to open it to work on it and the map was gone? If you had any type of issue like the crash or an outage, I’d start with this post Map dissapeared from Project. I hope this helps! If it doesn’t, post back and we can try to find the culprit. (Also check your folder and see if the map file is still physically in your project folder in Windows)