Strangely, my train depots won't allow me to buy any trains - engine, cars or multi-units. The 'buy' button remains muted.

I certainly have more than enough in budget and all depots are correctly connected to the rail network (I'm no stranger to Transport 1).

Have any of you experienced this? Thanks.

*Solution*
Nevermind, found the issue. Turns out TF2 requires 'adding' the unit to cart before purchasing is allowed.

If you want to buy multiple units like trains, you must click the "add" button that shown, when you hoover the mouse over the locomotive or wagon.

When you finished the assembling of the train, you can buy the train.

(Pardon my very bad English...)