That was it! The "or die"-addition!
I already checked whether the script was running in the correct directory, and it did. It turned out to be quite easy: The rights set on 'textfile' weren't right; Apache wasn't able to read.
Thanks Monks! You really helped me out!
The great mistake is to anticipate the outcome of the engagement; Let nature take it's course, and your tools will strike at the right moment.