Some time ago, I posted a message regarding my problem with a new chain I was trying to put on. It was the same number of links as the old chain, but turned out to be way too loose. After taking my problem to my LBS, he discovered that my Dura-Ace (old friction model) rear derailleur had "unwound" because a small pin holding the spring tension was missing for some reason. With no tension from the derailleur, the chain hung loose. He rewound the derailleur, put a new pin in, and I was back in business. Didn't even charge me anything!