Producer ISM, whose real name is Ishmael Sadiq Montague, filed a lawsuit against Sony in federal court in New York on October 16 over contractual royalties for Chris Brown's song "Party," which features Gucci Mane and Usher. According to the lawsuit, ISM agreed with Chris Brown Entertainment to take a 1.5 percent cut of the royalties, but Sony paid it an amount calculated at a rate of 0.75 percent. The company claims it noticed the error in July…