[Trouble shooting/Linux] Invalid file identifier. Use fopen to generate a valid file identifier.

This problem comes up when you make a mistake in programming.

e.g., wrong file pointer or something.

HOWEVER!!! You could get this error EVEN THOUGH YOU WRITE A CODE CORRECTLY!!!

In the linux OS, 'fopen' could fail in a location where your MATLAB does not have all the permission (e.g., write, read, etc.).

(In my case, I solved this problem by log-on the server computer as a root permission.)