One common thing that leads to this:
- check out and change a drawing, but don't check out related model(s)
- change something in the drawing that in fact get saved in the model
- select to Continue for the model
- check in the drawing
- next retrieval of the drawing (possibly by someone else at a later time), message log says "drawing is more recent than the model"
Have to check out the model to apply the pending changes stored in the drawing. These are "time bombs" in the system.