OK Upgrading to Sketchucation 4 has solved this problem. Thank you Dave. I'll ask sooner next time! I filled in the details on my profile, went back to the SketchUp Pro 2022 and clicked on the JPP. A text box came up prompting me to upgrade to the latest sketchucation and bingo it worked! (This box for some reason hadn't come up before..)
And JointPushPull did the trick straight away -such a versatile extension. I wanted to push/pull a vase shape out to give it thickness for a butterfly feeder I'm working on. I had been using follow me but never could guess the proportions for the shape it generated nor get a perfect solid. I really do appreciate these plugins especially this one - it makes things possible that just weren't before. Thank you for doing them.
Neil