Sorry for delay. I ran the patch overnight and it completed. However, when the game opened it just 'stuck' on the scenario/route page and then reported that Trainz was 'not responding'.
I uninstalled everything and reinstalled the game which completed as Build 42203 as before.(I expected to patch it then). However, for the past 30 minutes it has been scanning for added asset files and has only done about a quarter of its scan. I dont know what is happening only that Im reaching tear my hair out point.