Well, it seems that Atari has sub-licensed the Dungeons & Dragons rights out to Namco-Bandai, and Hasbro isn't too fond of that. Namco-Bandai is seen as a competitor to Hasbro's products, and Hasbro's contract with Atari specifically forbids them from doing any licensing like this. Namco-Bandai has recently purchased Atari's distribution wing in Europe, renaming it to Namco-Bandai partners. Atari is alleging that the lawsuit is "meaningless," and that Hasbro is simply seeking a way to take the D&D game rights away from Atari.
"Hasbro has resorted to these meritless allegations, in an apparent attempt to unfairly take back rights granted to Atari," said Atari in a statement to Gamasutra on Thursday. "Atari has sought to resolve the matter without cooperation from Hasbro. We regret that our long-time partner has decided to pursue this action. Atari will respond appropriately through its legal counsel in court."
Gamasutra is also reporting on the rumor that Atari is currently developing a Neverwinter Nights MMO in cooperation with Cryptic Studios, one of the issues that sparked the suit between Turbine and Atari.
One of the issues at hand here would be what could happen to Dungeons and Dragons Online if the Hasbro suit is successful and revokes the rights to the game from Atari. However, it's too early to tell exactly what may happen during the course of these suits.
For the rest of the story, check out Gamasutra's initial report on the legal filings.