This project is invalid or corrupt......

Hello. This thread is super old so I'm trying to figure out what the fix currently is. I have a file that gives me this delightful error, "The project is invalid or corrupt and cannot be opened. It may have been created in an earlier version of storyline."  I'm sure that is the case but Storyline is constantly getting updates. Why would a file be corrupt from updates?  Someone please help. This is a 4 module project and it make money for my company. The first two there were no issue. The third module and I get the same message. I download the file from one drive and place it on my desktop. Normally I open it, but I got this message. I tried opening a new project and then opening the project. I get the same message every time. Can someone please help?