I'm having this error 201 issue today.
I was playing perfectly fine a couple of days ago with friends, now I can't join a game with them.
I've narrowed the issue for me down to when joining game servers as a group, then when I leave group the issue persists, but after rebooting the game I can join games perfectly fine, until I group up with my friends again and then I get this error 201. But they can join the games together fine, I am the only one getting kicked out, however like I said I was playing the game with them both perfectly fine a couple of days ago.
So far I have checked for updates, updated Windows, added BF2 folder to my firewall exception list, verified the cash, disabled and re-enabled my NIC, checked for driver updates, flushed DNS, ran renewed network adapters but I still get the same issue, but I can communicate with them both in DISCORD and join and player other games with them perfectly fine.
There issue, for me, lies with the in-game group feature when joining a match.
EDIT:
The ONLY work-around for this is to let them join the game, and then me join them while they are in-game already.
This is not ideal and clearly demonstrates there is a fault with the group join mechanic.