A colleague made an aprx file and saved it to a network drive, I asked if I could look it over. They sent me a link, I open the aprx and receive the following error "Failed to Open Project: Opening the select ArcGIS project failed. This project was saved using a newer version of ArcGIS Pro : ."
This isn't true though, we are both running 2.4.0 - both of our installs tell us our versions are up to date.