Running version 17.2 of TC and v3.5 of CAM
It is not a work plane problem. I thought of that and made sure everything was on the current work plane. Also, the fact that reloading an earlier drawing, unchanged since successfully producing text G Code, will not work suggests the issue is not the work plane.
I an beginning to think you are right about reinstalling TC, as I have been plagued by unexplained and frequent crashes for some time now. This behaviour seemed to come about with ver 17. (Ver 20 was even worse unfortunately. So bad that TC kindly agreed to a refund due to this and that CAM would not work with the 64 bit version of V20)
Thanks for the prompt assistance. I shall reload TC (yet again) and report.