I would guess that the mex files were compiled for a version of OS X that is too old for your current system to use.  Deleting the .mexmaci64 file should allow it to function, the .mexmaci64 file is only there to increase the speed.  If I am correct, you may need to delete any other .mexmaci64 files as well.

However, note that the ft_ functions are not what the HCP recommends for loading MRI-based cifti files, see FAQ 2 here:

https://wiki.humanconnectome.org/display...

If you need access to more than just the data matrix (which is basically all ciftiopen exposes), we are working on a new toolbox, but it is still being tested.

If you are working with MEG data, you may have better luck simply installing the full FieldTrip suite, as it should be more up to date.