payment module freaks out

[parcelbrat]

This same question comes up 10 times a week here on the forum and is discussed in our FAQ's.
You will find it here:
http://www.zen-cart.com/forum/faq.ph...s+already+sent

You will also find over 12 million hits on Google for the same error message:
http://www.google.ca/search?hl=en&q=...s+already+sent

Cause:
The filename in the message has blank lines or blank spaces on the line-number indicated ... in your case, line 1 of includes/parser_php4.php

I didn't realize that I needed to start with the error at the bottom. Sorry for repeating a common question.