What causes an invalid file identifier in MATLAB?

Question

I have a MATLAB script that I could have sworn worked fine the last time I used it (a year ago). Now, I get this error:

Invalid file identifier.  Use fopen         


        

Answer 1

For my situation, I have checked everything, but missed an easy step.

Please select "browse your folder" and browse for your current document location before you run your 'fopen' code.