zewtastic on "Trouble getting wp_mail() to work"

I absolutely call this:

require_once( ABSPATH . 'wp-includes/pluggable.php' );

which includes the function:

function wp_mail( $to, $subject, $message, $headers = '', $attachments = array() ) {
// Compact the input, apply the filters, and extract them back out

No idea why it is throwing an error.

I have an SMTP plugin, but wp_mail fails with it active and disabled.