Only this time because I was doing other stuff I decided to create a Projects folder which contained the Asteroids folder and some other stuff and opened Projects as the Folder.  I copied the hidden .vscode folder into Projects/Asteroids and tried to compile. Errors. Lots of compile errors. I repeatedly edited the tasks.json file with altered paths but no joy. I spent an hour trying before closing the Folder and reopening it with Asteroids as the Folder and with the original tasks.json. It compiled perfectly.

So the moral of the tale is just keep the level of folders down to one when you open the Folder on the files you are compiling. Do not have subfolders.