Britney Spears has sparked further reports her marriage to Kevin Federline is in trouble, after she failed to attend his album listening party on Friday (21APR06). The couple and their seven-month-old son Sean Preston arrived in Las Vegas, Nevada, last week (ends21APR06), ahead of aspiring rapper Federline's gig at the Pure nightclub at the Caesar's Palace. Local newspaper the Las Vegas Review Journal reports the couple were spotted arguing in Caesar's Nero restaurant ahead of Federline's bash and Spears retired to their hotel suite in tears. Federline went on to perform two songs, AMERICA'S MOST HATED and ROCKSTAR from his debut album PLAYING WITH FIRE, after an introduction by Paris Hilton's mother KATHY. Federline entertained a few hundred fans, as well as celebrity friends, former Fresh Prince Of Bel Air actress TATIANA ALI and Kathy's husband RICK - but his superstar wife was nowhere to be seen.