Steam validation rejected??

[Cursed]

A friend and I are trying to make a modded server so we can play together and every time I try to start the game up it tells me that me steam validation has been rejected. Ive looked up other solutions but nothing had been straight forward about it and I have no idea how to fix this problem.

[Zombie Tsunami]

put your dedicated server on a seperate computer than the one that you are playing on. you will need to own two copies of l4d2 and have two steam accounts.

or you could host a local server with the addon Admin System so you don't have to have two computers and two steam accounts.

https://steamcommunity.com/sharedfiles/filedetails/?id=214630948