Good morning all. I’ve got a file with several mesh models imported from Sketchup 3d warehouse. I have exploded the blocks, successfully, but when I go to Block Manager to try to delete the Block Definitions I keep getting the message “Unable to Delete Nested Block Definitions.” There seems to be about 100 of them. Is there no way around this, please?? 
The Purge command will let you delete unused things in a Rhino file, including unused block definitions.
Thanks, John. You’re the mannn.