Why am I getting "Invalid MEX file: Library Not Loaded" error

The function I'm trying to use references a MEX file and I keep getting the following error:

Invalid MEX-file '/Users/aalonso/Documents/MATLAB/yin/private/rsmooth.mexmaci64':
dlopen(/Users/aalonso/Documents/MATLAB/yin/private/rsmooth.mexmaci64, 6): Library not loaded: @loader_path/libmex.dylib
  Referenced from: /Users/aalonso/Documents/MATLAB/yin/private/rsmooth.mexmaci64
  Reason: image not found.

I've never encountered MEX files before and honestly I'm not sure where to start.

Any help is greatly appreciated!

[Marta Karas]

I also need help on this issue.