I'm just a simple caveman lawyer, and your world of finance frightens and confuses me. However, it sounds like Viacom wants a refund on a substantial bonus it paid to Harmonix's founders.
Long story short, Harmonix was bought by Viacom, the parent company of MTV Networks, in 2006 for $175 million plus "earnouts," which is a jargony way of saying "beat previous figures and you get a premium." In this case, Harmonix got $150 million based on 2007 performance, and some $300 million overall since then. However, Viacom in this filing notes that the $150 million payment was subject to adjustment.