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Work needed: This is a planned topic, earmarked for future development
Trainz pre-compiled asset Libraries, *.JA files can be uploaded into the next generation Trainz in most cases, and with some limitations. In point of fact, cross loading assets sometimes runs afoul of a incompatibility of scripts in *.gs files when doing so, and correcting these issues can be vexing, as where what changed, and which asset needs which change to work with the newer more modern *.gs files is not always immediately obvious.
It takes a little sleuthing and trial and error, advice seeking on the forums, and is just a spot of bother when an older asset runs afoul of a new system. The problem is rarely serious, though it may block running a particular route for a few days whilst the matter is resolved. Normally, this sort of hidden fault will show as a faulty asset, normally with a KIND and Class message in the Content Manager.
After loading JA's it is therefore a good idea to examine all the dependencies of the 'added on routes' and a screenful at a time, re-validate them (check for errors and warnings of that whole page). While little repetitive, even working through a major route and it's sessions is straight forward. This requires regular waiting and evaluation of messages, but the wait times are surprisingly brief, albeit they will give you time enough to read a page or two in the Trainz Manual between gos. We recommend new Trainzer's do exactly that. Early in your Trainz career, you can't read the manuals often enough. Old hands will likely busy themselves working on that new asset they've got cooking. Just master ALT+Tab ⇆ and SHFT+ALT+Tab ⇆ toggling back and forth between applications, and if you're blessed enough to have two or three heads on your computer setup, run CM on one and use the other for whatever else needs done in the foreground process. Bumping the priority of CM during this process is beneficial to a speedier completion.
Tip: Remember - The new Trainzer is very unlikely to ever first discover a problem before a ten year veteran Trainzer! Use the informaton resource of the Auran forums!