Online Gaming and Rights

My husband created a codebase for a multi-user, non-profit online game, and gave it to someone who was running these kinds of games. My husband included in the license agreement (a .txt file sent with the codebase) that this person - I'll call him 'B' - could use the code as long as my husband's site was not banned or blocked from using the game. That was the only stipulation. He made sure B was aware of this agreement, and B accepted the code and used it for his game.
Lo and behold, B has now blocked my husband from entering this game, and won't remove the code he spent weeks, even months working on. This code was not copyrighted. Is there any legal action we can take to rectify this? All we want is for B to remove my husband's code from his game, or to turn the entire game over to us, since the game would not exist without the code. Is this even possible?
(Note: We are located in SC, B is located in CA.)

It appears the code WAS copyrighted (as a matter of US law and the Berne Convention) -- although the copyright was not registered.

You husband could demand that the user cease and sdesist from using the code. He could also file a copyright registration for the code on an expedited basis (that's costly), and then sue him in Federal court for violation.

But as it would take a lawyer, get some advice now.