I had no problems bringing in my route first created in TRS2004 and then updated to TRS2006 and to TS2009 into TS2010.
I did, however, and this is the important part....
1) Backup my content before I did anything!
2) Spent about a week fixing downloads using the various tools available. These included Peter Vincent's wonderful utilities, Notepad, and Gimp. This took as, I've indicated in other posts, some time to do, but all was not lost.
For many of the "broken" assets, the repairs were/are quick and simple. A quick run of one of the utilities, a deletion of a texture.txt file, a quick edit of the Config.txt to remove a typo, or attachment point of some missing passengers if it was a station.
I think I averaged about 250-300 assets per day, perhaps more. As time went on, I got better at it and the process became quicker and easier.
I also spent time and repaired most of the Warnings. The easy ones were simple Config file repairs and utilities from Peter.
All in all, I am down to about 30 "broken" items out of the 147,000 plus I have in my local file, and about 3600 old PS objects and others with PM meshes instead of IM, or whatever the meshes are that produced the warnings.
3) I also ensured that all of my drivers are at the latest that my hardware can handle.
I known there are mixed feelings about this, and I agree there are some things that work and those that don't depending upon the hardware. This is what makes computer support so difficult, and why I always say "should" instead of will when recommending a fix.
4) Have lots of patience when dealing with Trainz.
It's amazing how many people push their computers when running this program. By this I mean not waiting for tasks to finish before doing something else. Perhaps I learned this from my old CP/M days and single-tasking systems, but when a program is running something criticle, like a database repair, I go off and do something else.
Watching the progress bar is like watching water boil, so rather than be tempted to touch my computer, I'll do something more important like take a nap, or more importantly practice the piano.

I know that this process takes awhile so when I'm done doing my thing, I'll check my computer to see if the job has finished. If not, I'll do something else until it's finished.
5) When I get frustrated with the program, I walk away.
Yes, I do have snags, issues, and snafus. There are many here that I have not reported as problems, but have reported back to Auran for repairs in future versions. I've also used their experiences as a way to help others when I've resolved them myself. Like anything else in life, there are work arounds and ways around situations so that sometimes the worst things can be dealt with easily. Heck if you get hit in the head once too many times, you eventually learn to duck!
There are also some truly weird things that are still happening with TS2010. Part of it is my unfamiliarity with the software, and perhaps my way of doing things, but others are plain glitches that I am writing down.
6) Don't fight cityhall, and read other people's suggestions.
I come here to help others and to enjoy the company of the forums, I also keep in mind that there are plenty of other people here who are smarter than me, have been around here longer and have a lot more experience with life in general. I don't try to outsmart them with wise crack answers, or nasty comments. I read, try, and hopefully incorporate their experiences into mine. In many cases, other posters here have helped me, and I feel bad now not thanking them directly. I treat them with respect as I would expect from others.
7) Ask for help nicely.
There's no reason to get nasty and blame Auran, or get into a snit with the forum members. Granted Auran wrote the program, but getting nasty with them won't get anyone anywhere. The fact that the program works for a good number of people, means that isolated not working issues, are just that, and can be narrowed down to hardware or system problems.
8) Accepting the fact that nothing is perfect even in this so-called technologically perfect world.
I am amazed that this program can even run at all on the various platforms out there. Each computer system, even if it's closely related to any other one out there, is as different as mom's homemade cookies. Keep in mind that even though many people tested the program on many different hardware combinations, there are still going to be some flavors where things just won't work.
and most of all...
9) Remember it is only (ahem) a game even though it consumes a big part of everyone's life here including mine.
John