I hadn't done multiplayer for several months, but with the recent sale I bought a second copy of TS12 to install on my son's computer. That was when I discovered that NONE of the multiplayer sessions I had working last time I tried it would launch at all. Main problem is updates, if (for example) Chicago Metro V2 MULTIPLAYER TEST 1,<kuid:522774:100174> was working perfectly and is not now, gotta check all the dependencies and sub dependencies to fix it. In this case mea culpa - I made that new "brakeman view" and uploaded KUID2 replacements for a bunch of cars, ChiMet FREIGHT LD 40 ft Boxcar A,<kuid2:522774:100126:1> is now ChiMet FREIGHT LD 40 ft Boxcar A,<kuid2:522774:100126:2> and requires freightview XP 5,<kuid:522774:100089> which the previous one didn't. I HAVE all that stuff since I made it myself, problem is the pedantic rules which require everything on the DLS and nothing locally modified, so I got a lot of deleting and redownloading to do. I managed after a full day and 90 megs of downloading to get Chicago Metro V2 CTA multiplayer 16 30,<kuid:522774:100225> working on both machines so we did get a chance to chase each other around the elevated and subway system, so I can confirm that the server is working fine.
The problem is the basic design of multiplayer needs to be reprogrammed to remove many of the restrictions that cause more problems than they prevent. Joe starts a session using a heavily modified steamer with lots of smoke, people joining the session have the original unmodified steamer so they don't see the same smoke Joe sees, so what? Bob joins the session with a GP38 that has sliding disk wheels when everyone else has the KUID2 replacement updated for rolling wheels, so what? Redesign the blasted thing so that if all the basic KUID numbers match it will launch, if a joiner is missing dependencies smack him with an error message. If a bunch of guys try to play Thomas the Tank Engine on the Island of Sodor and nothing used is on the DLS, it should be THEIR responsibility to make sure everyone has all the parts needed and do their own debugging if someone doesn't.
The THEORY behind the restrictions was very noble, make it easy for n00bs so a lot of people would be using multiplayer, but in actual practice it ain't working - people are staying away from multiplayer simply because the automatic restrictions take too much time and effort to get a multiplayer session started.