Hi Anna,
Thanks for your reply. To clarify, I use the Bezier tool to draw polylines and polygons and often, as I have mentioned, the area covered by the map is large - country scale or larger, so there are many 'arc'. Continuing to zoom in before the trace tool would work again is of no practical use. ESRI did reproduce the error, which seems to have geographically bound component i.e. affects particular parts of the map *only* once it decides that it doesn't like that area. I can't define anything special that I do to cause the trace tool to fail - it seems to be random and can happen sooner or later in the compilation process.
I use the Bezier tool as it is quicker and more intuitive for drawing geologic unit shapes (for me at least) that will rarely, if ever, have a straight segment. I also use the equivalent tool when I draw in a vector graphics package, so it's always my go-to tool. Maybe if I only used straight line tool with the attendant issue of increasing the number of mouse clicks by orders of magnitude, the problem would go away...
I have tried a couple of suggestions in earlier responses to my original post, without success. I had effectively given up and used my work around - draw a polygon through existing ones and then clip it using those existing polygons. It's a pain, but work and is good for ensuring the topology is ok.
I'm on a much needed vacation at the moment, but over the next 3-4 months will be compiling several more maps and will try all suggestions again and report back.
Thanks for taking the time to post.
Cheers!