Just making a string variable with the folder the files are in doesn't help. You need to actually change the directory in MATLAB. You can do this with the cd command. However, if the program isn't in that folder you may get problems when you change the directory.
Another idea is to put the full file path in the load command, like this: load('/Volumes/MY PASSPORT/redhwan/Documents/MATLAB/2DimenstionalTestingGT20150907/MeasurementDataFinal/TWDPN5db14ft_35inchMetalCabxpositions.mat')