Don't yell at me if you already know this,but it won't work cause' it has txt. at the end. I have the soultion! If it doesn't work becasue of the .txt part just quit srb2 (becasue it will say something is using it) then go to the wad and right click it and click "Rename", then when the name goes gray or whatever, go all the way down on the name and remove the .txt part! It will say this something like this, "Are you sure you want to rename this? It will become unuseable." Just click ok or Yes and then turn on srb2 then enter addfile <Insert the soc or wad here> and it should work like it did for me.
(Useless P.S)
This was like the most longest sentece I typed in my whole entire life!!!