Not a valid project file

My son has created several animations. Sometimes after he saves his animations and goes to work in them again, he receives the error code "not a valid project file (e1119). Can anyone help?

This sounds like the projects may have become corrupted.

Your son should work on projects only when they are located on the internal hard drive of the system. He can move projects to external drives and USB drives if the project folder is zipped first. Only the system’s internal hard drive is responsive enough to keep up with the data being generated/manipulated.