San Diego-based MP3tunes, the online music locker service started by Michael Robertson, has filed for bankruptcy, according to documents posted to the web by an ex-employee. According to Robertson, in an interview with CNET, the bankruptcy filing came due to overwhelming legal costs to fight a battle with EMI. EMI sued MP3tunes in 2007, accusing the firm of violating its copyright. The bankruptcy-due-to-entertainment-studio-lawsuit is not an unfamiliar one for Robertson, whose most famous startup, MP3.com, was sued by just about every label out there before succumbing to bankruptcy. Robertson is no stranger to long legal battles; he's battled former employees (which sued Linspire), Warner Bros. (which sued AnywhereCD), Microsoft (Lindows, forced to rename itself Linspire), and the RIAA, Universal, and others (lawsuits against MP3.com), the Del Mar School District (filed by Robertson), and Vonage (sued by his firm SIPPhone). Despite that, MP3tunes did pave the way for similar online music locker services like Amazon.com and Google's own.