[exim] setsockopt(SO_KEEPALIVE)

I have a *vague* recollection of having seen a post on this sort
of error - but am not even usre it was on the Exim list:

2006-04-14 12:21:14 SMTP connection from [220.194.14.66]:16860
I=[203.194.153.81]:25 (TCP/IP connection count = 2)

2006-04-14 12:21:21 setsockopt(SO_KEEPALIVE) on connection to
205.158.62.181 failed: Bad file descriptor

Can anyone point me to the thread?

Thanks,

Bill

FreeBSD 4.11_STABLE, Exim 4.54 (on that box only)