Disallowed characters in mime headers

From: Take a Walk (spam_at_hotmail.com)
Date: 01/29/04 

Date: Thu, 29 Jan 2004 16:51:28 +0000

I use php to send email and get some bounces saying I may have a virus,
because of disallowed characters in mime headers.

Here is a sample returned mail header section, anyone know what is wrong?

Subject:
From: Sales <sales@mach.co.uk>
Reply-To:mailreply@mach.co.uk
MIME-Version: 1.0
X-Mailer: PHPBulkEmailer 1.1
http://www.nukedweb.com/
Content-Type: text/plain
Content-Transfer-Encoding:8bit
Message-Id: <E1AjhQK-0001ft-00@mail.mach.co.uk>
Sender: Apache <apache@mail.mach.co.uk>
Date: Thu, 22 Jan 2004 16:11:16 +0000

cheers