The download precache thing is just a warning disregard those.
Have you tried other track assets?
Have you tried your current assets on a test route?
Something could be wrong with the assets you are using or the track. Perhaps the assets were updated and this caused the problem. I had what were once tracks become splines, as in roads, because they were updated. I also had factory buildings become canal locks on one route because someone had typo'd a Kuid and I downloaded the asset.
Some things to think about. FYI... in the future you should mention you are using T:ANE as this helps in troubleshooting as each Trainz version has its own bag of worms.