My Ctrl key doesn't work in multiplayer games!
The Ctrl key only works if you use the latest TTDPatch, 2.0.1 alpha 10 or later. Earlier versions were not able to transmit the use of the Ctrl key to the other computer, and therefore it was disabled to prevent desynchronizing the game.
My games has become desynchronized! What do I do now?
First of all, if you are using TTDPatch 2.0.1 alpha 10 or later and have made sure that your configuration files are identical on both computers, any reproducible desynchronization is a bug and should be reported as such.
If it already happened, you can use the SV2flip tool to resynchronize both computers and keep playing the game.
How can I play stable multiplayer games?
You need the latest development version of TTDPatch, at least 2.0.1 alpha 10 or later from here. You also have to have identical configuration files (including identical files for new vehicle graphics) on both computers, as well as a fast (low-ping, ideally <10 ms) connection. Unlike earlier versions of TTDPatch, multiplayer games should be quite stable if you have alpha 10 or later.
Why can't I play multiplayer games in full-screen mode?
(This applies to the Windows version only.)
When initiating or joining a multiplayer game, TTD switches back to the Window interface to display the multiplayer game selection dialogs. After the game has been set up or selected, the game should return to fullscreen mode. However, this doesn't work correctly on many (most?) graphics cards, and the game cannot be resumed at all. If this happens, one of your options is to choose windowed mode in TTD's configuration program, or if you choose 'Mode 4 - Full Screen - Game's mouse pointer' in the configuration program it should work correctly. The default display mode is Mode 5.