bash: cannot execute: required file not found

bash: cannot execute: required file not found

The problem, it turned out, was an incorrect path in the shebang.

#!/bin/bash

echo "Hello, World!"

will fail on a machine which does not have bash at /bin (or a link to bash there). I believe cron jobs also have problems if the shebang does not directly point to bash? Anyway, we can always do a 

which bash

to find the correct path and enter it in the shebang.