Unable to save civil dwg

Hi everyone, hope someone has come across this. I work with autocad 2020 and I received a file from the civil engineer, for some reason when I make simple edits to his drawing like changing colors or deleting junk he has on the drawing it will not allow me to save it. I get a message "One or more objects in this drawing cannot be saved to the specific format. The operation was not completed and no file was create.". I deal with civil drawings all the time and have never come across this problem. Looking forward to a solution for this. Thanks in advance.

you are running 2020, what's he running?

Problem solved. Working with the civil engineer it seem that one of the surfaces in the file was created by a point cloud in version 2017. The point cloud features of cad went away in 2018 and subsequent versions, but the file still thinks a point cloud is associated with the drawing. So the engineer copied all the contents of the drawing and pasted them into a new drawing which fixed it. Hope this helps anyone who comes across this.