every time process cant bee start program succefully close error

As the title. Just looking for players to play with.

I downloaded the Killing Floor - Toy Master Mod successfully without any problems BUT here comes the problem...I press the "Play" button on the Steam Library and instead of starting the game it opens the Folder in which the Killing Floor App is inside the Steam Folder and at the same time an error report appears on Steam saying : Failed To Start Game (Unknown Error) See the Steam Support site for more information. What can I do? Please help me!...

it says unknow error than opens the files for the mod

I don't know why he say that and i think there is nothing we can do if you can i will not forget you all my life! <3