Just to be clear, there have actually been squad-creation problems recently which were not user error. We played half of a map last night where the USMC had 25 people in squads and a steady rotation of 5 squadless people who could not play.
This may be a stupid question.... but are you alive and spawned in the game when you try to join a squad? From what I understand, the 1.3 patch enforces only live spawned players may join a squad.
I have had the problem when first joining a game. I have had the problem when trying to switch squads mid game. Of course on other servers I can still play and I noticed that most if not everytime a map ends, I am able to squad up. With our server I get kicked of course so I don't know if a map change would fix the problem. I have joined our server, had the problem, spawned solo, killed myself and still can't join a team, respawn and try to squad up while alive and no luck.