I had trouble converting my large raw AVCHD files into FCP using the Log & Transfer tool. FCP would crunch on it for a while and freeze up or try briefly and give me a "no data" issue, although my video appeared fine in the preview window.
Looking through the COW, I found Shane Ross recommend a program called Clipwrap. It's simple, easy, super-fast and bailed me out! It will also take it to few different file types including dvcpro hd if you don't edit in FCP.
$50 makes it worth it for the additional speed it offers. They also have a free trial if you wanna give it a test run. If you work a lot with AVCHD I would definitely recommend checking it out. Cheers!