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

Nope. Like most companies, we store all of our files on a shared drive in the cloud. We download the files to our desktop when we work on them. What makes this case unique is that my coworker can download and work on the file, and I cannot. We both keep our Articulate up to date, but apparently one slide is corrupt for whatever reason. Supposedly, the issue is because my version is more up-to-date than his version is but I don't see how that's possible since we both download Articulate's updates as they come. Maybe he hasn't though. Either way, I wouldn't expect updates to create corruption but in this case it did.