According to this Bloomberg report, Konami has sued EA over patent violation related to Rock Band, claiming the game violate patents filed by the firm in 2002 and 2003.
The Konami patents, relate to simulated musical instruments, a music-game system and a "musical-rhythm matching game."
What does Konami want? Muchos money, amigo. And the other small prize of being able to block EA selling products based on the technology Konami claimed it stole.
The suit also names Harmonix Music Systems, Viacom and MTV.
More through the link.