Did you put in your project folder all the folders that comes with the recording and not just the movie files?
In case not, you may try that.
(the all AVCHD folder and sub-folders.)
Normally you should be able to read the MTS files without rewrapping but when they are located within the entire AVCHD folder. Something similar happens in Avid.(previous of 6).
Premiere and Edius would just read directly the MTS file alone but not FCPX (that I know, please correct me if this is wrong) nor Media Composer pre-6, they need the all folder structure.
So instead of bringing individuals MTS clips, you'd need to have your AVCHD organised copied in your project.
I generally do folders that correspond to my cards numbers.
I name them "1", "2" etc... in "1" I put the entire AVCHD folder recorded in card 1, in "2" the entire AVCHD folder from the card 2 etc...
As it's always the same folder name created by the camera each time it records, AVCHD, you need to find a way to not overwrite.
nota: I don't currently edit with FCPX, so the solution I'm pointing here may or may not be the right one, but it's a solution to try anyway because it's a common case.