I just tried that one, downloaded in CM 3.5 for TS12, got the following when I checked for errors and warnings;
Warning: This asset uses an obsolete trainz-build number. Trainz-build numbers below 2.7 are no longer supported.
That can be safely ignored, just because the build number is no longer supported doesn't mean it won't work. Some build numbers that ARE currently supported don't work anyway, and they're not in any kind of hurry to fix those.
Error: Attachment point 133 (a.hay133) in 'queues\hay_q\attachment-points' was not found.
Error: Attachment point 147 (a.hay147) in 'queues\hay_q\attachment-points' was not found.
Error: Attachment point 152 (a.hay152) in 'queues\hay_q\attachment-points' was not found.
Error: Attachment point 157 (a.hay157) in 'queues\hay_q\attachment-points' was not found.
Error: Attachment point 172 (a.hay172) in 'queues\hay_q\attachment-points' was not found.
Error: Attachment point 177 (a.hay177) in 'queues\hay_q\attachment-points' was not found.
Error: Attachment point 214 (a.hay214) in 'queues\hay_q\attachment-points' was not found.
Those are actual error errors, the original creator made some kind of mistake or the attachment method is obsolete. Looking at this one I would say the former since it has a lot of attachment points and only a few are missing.
First step, right click the asset, select Edit, then Edit in Content Creator Plus.
You'll get a warning message about obsolete build number, but since we intend to update it anyway, click okay to get past that. At the bottom is the list of error messages, since this one is multiple instances of attachment points look for attachment points, find the ones highlighted red - those are the ones it's calling for that aren't actually in the mesh. Easiest way to fix that is to just click the X on the right side to delete that call for the non existent attachment point. Save, look at the error messages at the bottom again. Once those are all gone, save and exit, back to content manager, select the asset you just edited and saved. Right click, select Edit, then Commit. When that finishes (the open for edit icon disappears) select and right click again, view errors and warnings. Probably get some, since what were acceptable tags for build 2.2 are obsolete for the new build I just converted it to, I got "tag Icon 0 is obsolete" and had to edit again to get rid of that. Save again, commit again, check for errors and warnings again, this time none.
And then see if it works in TS12.
Be advised this works great for your own personal use, but if you intend to upload the route it won't be very good since you'll be asking the end users to all individually update this thing before they can use your route. And of course there's no way it would work for multiplayer. Two solutions for that, get the item added to the DLS cleanup project and upload a KUID 2 of it, or clone and upload your own version and use that in the route instead. Be sure to ask permission before uploading your repaired version or you'll have the Self Appointed Internet Weenie Police over at your house checking to see if you tore the tags off your mattresses.
