According to Mangaoh, the second movie of Mahou Shoujo Lyrical Nanoha will be announced at Lyrlcal Party IV to be held on November 23rd. The second Nanoha game will also be released and the new characters of ViVid and Force will join the game.
Source: Mangaoh
Update
According to MyCom Journal, “Mahou Shoujo Lyrical Nanoha The Movie 2nd A’s” will be premiered in 2012.
Source: MyCom Journal