Julia - is your compiled MATLAB function named function.exe and are you calling that from the command line as
function.exe 'C:\Users\name\datei.dat'
If that is the case, how are you using the input in your code? Do you break it apart into the datpath and datname only to rebuild it when you call
fid= fopen(fullfile(datpath, datname));
Looking at the first example http://www.mathworks.com/matlabcentral/answers/92537-how-do-i-pass-arguments-into-and-out-of-my-standalone-executable it appears that you may not need single quotes around your input string.
I would add fprintf calls in your code to write out what your datpath, datname, and fullfile(datpath, datname) are set to.
