Originally I wrote some PHP code in the “PHP Method” section, and called the method from an Ajax button. Inside the code I use an accented character as part of a filename for fopen function.
Later I moved the code (cut/paste) directly to the Ajax button, and the page started to fail with a “file not found” message.
Checking the deployed files, I found the problem: the accented character was not encoded the same, it changes from one editor to the other.