Custom Field in Email Template - only works in Subject, not in body

Hi,

Ive been trying to use this guide to insert custom field values into email templates. The problem is that it only works for the Subject and not in the body of the email template.

When inserting the custom field code into the subject it TURNS YELLOW and is working perfectly when using the template.

When inserting the custom field code into the body it DOES NOT TURN YELLOW, and is not working when using the template.

Any ideas why this is happening?