Voidtrain
Wagon Limit Reached
Ran into this problem while completing the "Breaking In" quest and wanted to share the solution for other new players. When pulling into the station for this quest, we had three wagons (I think, the UI leaves a lot to the imagination). We had also researched the Steam Engine and wanted to place it. So, we removed the Train Handle and spent far too long faffing about trying to place the Steam Engine, but were not able to. We also could not upgrade the wagon again "Wagon Limit Reached" or add another wagon as we did not yet have the orange lunch box. So, we searched the station and found said orange lunch box and went back to add a wagon. But, we were faced with the same "Wagon Limit Reached" error in the "Add Wagon" button. With no clear indication what the problem was.

We thought it might be a bug related to me picking up the orange lunch box. I am the second player and the item did not appear in my inventory. We also thought it might be something we needed to research still. Or, maybe we got ahead and should not have fully upgraded the wagon in previous stations. But, it turned out to be much simpler, though not obvious. Remember I said "we removed the Train Handle"?

It turns out, that the lack of propulsion source means that we are limited in the number of wagons we are allowed to have. I had to add the train handle back to the train to let us build the next wagon. Then, we were able to move all our stuff to the new car, re-remove the train handle and plop down the steam engine.

It makes some sense, now that I know the solution. But, maybe instead, let us build to the limit of the train handle, even when it's gone, and just not let us leave the station (and maybe have the Narrator say, "hey stupid, you need a source of propulsion to move your train"). Instead of leaving us wondering what the hell we are missing.