Ok first off make sure you have patched your game to the latest version. If not go here and download this - http://games.softpedia.com/get/Patch/Mount...and-Patch.shtml
Once you have done that and you have patched your game, you then want to put in the installation folder the mb_dedicated_server.exe which you can download from here - http://www.taleworlds.com/ just go to the download tab and scroll down to the file. It will say that you don't need it to join multiplayer games, but if you can't connect then you do need it so download it. Then put it here -
Re-Cap - You have patched the game to it's latest version and you have put the mb_dedicated_server.exe into your installation folder. C:/Program Files/Program Files (x86)/Mount and Blade warband
Ok the next step is to edit some files. SO, you want to go to C:/Users/USERNAME/My Documents/Mount and Blade Warband then the rgl_config.txt is the file that you will need to edit.
Once your into the file, press Ctrl+F and in the little search bar that pops up search use_secure_connection.
Once you have saved that, the multiplayer should work. If it doesn't then there may be another rgl_config.txt file in another Mount and Blade warband directory. Just change that use_secure_connection to 0 aswell then it will work.
Thanks for reading my guide folks.
Barnsey.
Copyright - The pictures used are copyright of Barnsey, don't reuse them for your own use.