Lesson learnt, always post the full code. Unless like MI6 chief's wife, it's secret.
New Sprite is because I forgot to comment one out after constantly switching lines to test. Code attached.
All worked fine using only the cw sprite direct in the destination collision sub. Not sure how (I didn't prefix with gw.), this can be seen by commenting lines 32, 38, 39, 40, 46.
However, as it stands now...
Enabling line 32, disabling 38 causes the error requiring New.
Line 40 causes the current error.
I obviously don't fully understand something about the passing of the sprite to avoid
gw.cw.ID I see the need but have somehow...?
A question out of interest. When the sprite goes around at a higher velocity, say 5, the sprite overruns the destination. I understand that it steps multiple pixels and may miss, so that a later pixel in the sprite 'arrives'. What I don't understand is why it only does it in this case, while travelling in directions 0 and 90 while 180, 270 are still perfect. Are you able to suggest?