Can't create LAN server

Im trying to make a server running gm_mobenix_v3_final so me and my bro can play but while it is creating it stops and goes back to the main menu it also happens on my brothers PC.

Does this happen for anyone else and is there a way to fix it i wanna party with my brother then nuke him while hes dancing lol!

does anyone have any idea what i can do i really want to play gmod with my brother

please help!

Did you try to start lan server on construct and change to mobenix?

Console: map gm_mobenix_v3_final

no because whenever i try create one it goes back to the main menu wtf is it doing that for

plz someone help