iPhoto problelms on multiple computers

I have owned a Mac since my 512K in 1986, and handled tech support for my classrooms full of Macs for over 20 years, but I am totally stumped here. Today in my office when opening iPhoto on a Mac Mini an error message came up saying iPhoto would have to be upgraded to open the library. There had been no changes to the computer and no new photos added since iPhoto was in use hours before. Well, there is a lot of info out there on how to solve the problem and I can work on those suggestions. But here is the real problem I need to solve. Before the day was out the same message appeared on two other computers--a second Mac Mini and an iMac. These computers have different operators, different versions of OSX, and different versions of iPhoto. What could be the common denominator that would make this happen at the same time on multiple computers. They are connected to the same network; they are not on the cloud.