if you get a black sgreen after choosing your opponent and then get the opponent list up again but can't click on anything, try disabling or removing Microsoft Silverlight. Worked for me.
Start game, go to coliseum, click on fight, game window goes black for a few seconds then goes back to the opponent list and I am unable to click on anything.
 "Turbo Golf"){kind=icon}
 "Sands of the Coliseum"){kind=icon}
 "Burrito Bison Revenge"){kind=icon}
 "Car Jump 3D preview version"){kind=icon}
 "Moto Trial Fest"){kind=icon}
 "EVIL KNEVIL"){kind=icon}