How do you add a wad file to srb2 everytime i put it in to the the launcher it says run time error 53 could not find file

Try Going In A Game/Match/Server(Make Sure You're Host) And Type This Into The Console. 'Addfile (Wadname).wad'
It Should Then Add That Wad Into The Game....
(NOTE: For Single Player You Must Add In Title Screen. You Cannot Switch During A Singleplayer Match, Unless You Activate And Deactivate Splitscreen.