Argh, head, meet desk. Sorry for lashing out with my last question, shouldn't answer questions when sleepy.

As for your problem, the type of text/plain shouldn't affect execution in any way.

The shebang line (the one starting with #!) should look like one of the following:

• for Bourne/POSIX-Shell compatible shells: #!/bin/sh
• for Korn-Shell (ksh): #!/usr/bin/ksh
• for Bo(u)rne-Again-Shell (bash): #!/bin/bash or #!/usr/bin/bash