I use msmtp as sendmail, and it takes quite a while to terminate
because doesn't exit until the remote SMTP server accepts the message.
Anyway, while msmtp was running, I moved my darcs tree from
darcs-make--tmp to darcs-make, thinking that darcs send wouldn't care:
why would it need to change directory?  Apparently I was wrong, as the
transcript below shows.

$ darcs send -p 'of trivial' http://darcs.net/unstable --all
Patch bundle will be sent to: droundy@darcs.net, darcs-users@darcs.net

You need a passphrase to unlock the secret key for
user: "Trent W. Buck <trentbuck@gmail.com>"
1024-bit DSA key, ID 24EDC406, created 2006-12-06

Waiting for Emacs...
Successfully sent patch bundle to: droundy@darcs.net, darcs-users@darcs.net.
darcs: /home/twb/VCS/darcs-make-tmp: setCurrentDirectory: does not exist (No such file or directory)

$

Moving darcs while it is running is not in general safe (although for commands
like send it shouldn't cause any trouble).  We often use absolute paths to keep
things simple so we don't have to keep translating things when the current
working directory changes.

Another alternative, of course, would be to never change the current working
directory, but that would be a major rewrite.

I don't think it's worthwhile to attempt fixing this.  Sorry!