Try This.
I do this for CMP. Not sure about CM2 or CM (UTC and 2004).
Go into your Trainz folder and look for Assets.tdx. If it is there, delete it. Then go into Cache. If Assets.BKU is there, delete that also. If you can't find Then open up CMP and leave it for a while. Maybe go have a drink and a snack. If you have a lot of content, this may take a while.