Yeah this has been an issue on many forums. I’ll cut and paste the solution:
Use Disk Utility to save your SD card (or camera hard drive if you have one) as a disk image. Then open the disk image and try Log and Transfer. FCP should see the disk image mounted on your desktop or external firewire harddrive and import the files. This works with AVCHD/.mts files. Plus, it gives you a nice small(ish) backup file of all your footage.