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

I had this problem. It turned out that the file I was trying to write was too large (I didn't have enough free space to accommodate it). However, the program didn't fail until the call to fclose. Very confusing!

Try freeing up some space, or writing a very small file, to test this diagnosis.