Reinstall Trainz Man Or Buy A New Copy
No, that is not what you do!
As I have said with anyone, when you don't get reaction from CMP, leave it for a length of time, like 30 minutes, because it seriously takes that long to search for assets. My 4 year old laptop has taken 45 minutes to rebuild the TAD, due to the amount of content it needs to find! (And most of it is mine anyway! ;-) )
Patience is a virtue, although, I've had 2 PCs simultaneously rebuild the TAD, because CMP has crashed.
Faulty content... as already mentioned, move the local folder out, then recreate one, then start adding in all the content from the (old) local folder to the new local folder, deleting the assets.tdx and starting CMP evey time you add something. (You could try something in bulk, then you know which ones it is likely to be.) This will take some time though.
The other option, is under explorer, navigate the local folder, then under the menu of view, click details, then arrange as date modified. If you sort the folder list to the latest ones you added, select them and drag them out of the folder by pressing shift (place them in a new folder on the desktop for now). Then rebuild the TAD.
Obviously, you don't want to remove your items, so go into each asset and open an instance of notepad, then click and drag the "config.chump" file into the notepad window.
At this point, the Chump file won't make sense to you, don't worry, they won't! What you are looking for, is clues it is yours, try looking for the description tag and everything after it.
When you are done and you know its yours, copy it back and see what happens. Just DON'T modify the chump file, or it may crash CMP again.
It is also worth noting, do not mess with the local folder, Auran and I do not recommend it, because there is so much that can go wrong with your installation.
HTHs, unlike the user above me.