Saves Disappearing

So I’m having a problem with saving my projects. I’ll work on one for a few hours, click Save As and close the application. The problem is, whenever I open the application back up and go to open the same file, it gives me an error message saying that the file doesn’t exist. I’ve looked in the program files, in separate places it could have saved, even in my recycle bin, and I can’t find it anywhere. This has only happened to me with a few of my projects- it seems like it doesn’t want to save the really long ones. I’m not sure if this is a problem with the application or if I’m doing something wrong, but it’s really frustrating to not have my hours of work save. I’m using the Basic version, so I didn’t know if that had anything to do with it.