Thanks for your reply.
Now fixed, I found a couple of duplicate lines.
I saved,shut and reopened the file as it still wouldn’t extrude properly,
until I turned off all the setout layers completely(they had the half light on) (which were showing thru in the extrusion although not in the scene).
Once it extruded properly I turned these layers back on and now it still extrudes properly.
This seems to be a problem (since Rhino6 ?) I have sometimes with the layers thinking they are still on when they look turned off.
Still sad the join function no longer works on crvs and blocks combinations, as it did in Rhino5, it creates extra curves from the blocks and sometimes from the setout layers,which are off.