Hi Scoobs,
This sounds to me like you have a corrupt packet in the inbox, or a corrupt / partially built packet in the outbox.
This can take a bit of tracing, so I won't try and describe the fix here. If you wish to speak to me on the Phone call 01635 570970 and ask to be put through to Nick and I will help you with a little bit of diagnosis.
Regards
Nick Welburn
CABC Support Manager