It's pretty obvious that what HH is trying to do is forward whole or part threads as email atachments... And as suggested above, thread size MIGHT be an issue...
It would be much easier to simply copy and paste the url (The HTTP://blablahblah bit) into the 'body' of the email.. that way you send a LINK to the information without actually sending a copy of the whole thread...
One assumes you know how to copy & paste HH? If not I'm sure someone here will be happy to spell it out for ya!