Most of the time it means the file was opened from a network source location, and the network connection dropped one or more times since the file was last saved or modified. (InDesign was unable to read/write from/to the file's location.)
As far as I know, the only way you can be absolutely ceratin to avoid the condition is to only work on a local copy of the file instead of working across the network. If you're already doing that and seeing this error, you may have one or more hardware failures looming.
Thank you. Yes. That is what was happenning. I seemed to have fixed it without even knowing 100% what I was doing.