OK so I've been working away moving scenery around etc. I've no idea what's changed but I've just managed three successful loads in a row. The last steps I did were remove three large OSM files from the custom scenery + the scenery_packs.ini file. This resulted in it starting. I then replaced, one by one, each osm file, restarting each time. Finally I replaced the original scenery_packs.ini It seems to work for now... Andy