Collectible Card Game Headquarters

HI sorry if this has been asked but i can not get x-mage to work, please be take some time with me as i am useless with computers.

I would be greatful if you could give me a step by step on how to fix the issue.

When trying to Launch Client is says "COULD NOT LOAD MAIN CLASS PUBLIC"

Are you trying to start the launcher or did you really install successful java and xmage and get this message as you try to start the client with the opened launcher?

Exact message (best with screen shot) would be helpful.