I've had occasional issues as well, but not too often.
The errors are pointed out due to the increased error parsing. This is why a misplaced quote will cause an error just like something spelled incorrectly, or if a container is built incorrectly. With previous versions of Trainz, especially with TRS2004 and before, the Jet engine would "horse" through the errors and load the content anyway. The problem with this is there is more work to do causing major stutters, like there aren't enough already, as well as outright game crashes when the program can't figure out how to get past the errors. By making the code "cleaner" right from the get go, the program will actually be more reliable and more responsive.
Regarding the broken payware....
If you have upgraded to SP1, JR has supplied some updates to their content. The SD70 was easy to fix if there is no update for that item. The asset it refers to is missing a thumbnail, which is now a requirement in TS12 SP1 and up. Simply create a thumbnail image and put the appropriate code in the config.txt for the faulty item. You should be good to go after that.
John