Gmod server issue

This is not me having a problem, but a friend of mine. Just trying to help him the best way possible.

Well long story short.
He tries to start an online server but gets this error
Then i try make a server. He cant join.
He makes a lan server. I can find it, but cant join (class c)
I make a lan server. He cant join because of the class c.

now, is there anything i’ve missed ? some setting that i need to apply ?

2 notes before ending the post.

  1. We both have Hamachi running in the background, therefore the lan thing.
  2. We both bought Gmod through Steam, so no illegal copies here…