What does this error message mean?

RESULTS OF VALIDITY CHECK

Problems were found that could not be fixed!

The entity at address 4d1cd0 has an invalid id (0) destroyed (0)

This message pops up randomly but does not seem to affect my work flow.
Any ideas what it is?

It’s a somewhat unhelpful message about an error in SketchUp ‘s model data management. It should not be possible for an entity to get id 0, so when it happens SketchUp deletes the offender because it isn’t able to tell how it happened.