Cannot import AVCHD into final cut pro x
If the contents of the AVCHD have been altered or become corrupted, FCPX may be unable to import it. Utilities such as Panasonic's (free) AVCCAM restorer will attempt to reconstruct the AVCHD file structure. Backup your file before you attempt it. 

In the event that the software cannot restore the file, it may be possible to extract the .MTS / .M2TS files from within the bundle, make a copy, place them within a folder, and seek to restore the contents of that folder separately. 

There are also utilities such as FFMPEG that can easily and almost instantly convert stream files (for example the individual .mts / .m2ts files) and re-wrap them as .mov files. Be aware that converting stream files directly to .mov or .mp4 files may lose useful information which would normally be present within the AVCHD structure.

Panasonic publish various utilities for AVCHD and AVCCAM file structures on the Panasonic pro camera download site.