Excerpts from Marc Hartstein's message of Tue Apr 26 13:03:19 -0400 2011:
> Something happened causing sup to crash, and now I get this exception
> every time I try to start. I'm currently tracking master.

Finally got it (though that outgoing message is lost because I foolishly
deleted it earlier; but that's ok, it wasn't that important anyway).

The message_id for the problem message appears to have appeared twice in
a row in the index. This caused find_docid to fail, ungracefully. Going
into the devel console, finding the message id, and doing
Index.delete("<message_id>") appears to have cleared things up nicely.

I believe the problem may have been caused in the first place by my
impatiently pressing ^L while a message was still sending. Not sure why
this would have this effect, but that was what I did when it crashed.
The outgoing message was GPG-signed, which might be relevant.

Sorry I didn't think to preserve the message for analysis. Although it
appears it made it out to gmail and out to the recipient (and it looks
fine).