Please help with email problem?

Hi
I have one address in my address book that i am unable to send emails to i keep getting following message.

Your message was not delivered because the destination computer refused
to accept it (the error message is reproduced below). This type of error
is usually due to a mis-configured account or mail delivery system on the
destination computer; however, it could be caused by your message since
some mail systems refuse messages with invalid header information, or if
they are too large.

Your message was rejected by mail-in.freeserve.com for the following reason:
Error: Message content rejected

Please reply to Postmaster@business.ntl.com
if you feel this message to be in error..

Is this a bug as i have tried every way possible to overcome this without success including getting contact to send me email and then copying address into address book.
Still the same result.
Neither i nor recipient are with NTL ????????