[Exim] lmtp errors

We are having some problems delivering messages using lmtp. Can I start
by asking what the following error is likely to indicate?

2001-02-14 10:51:57 14SzKm-000303-00 == adssdw@???
T=local_delivery_cyrus_lmtp defer (-1): LMTP error after end of data:
451 4.3.0 System I/O error


-------------------
P Christie
ccsphc@???