SBCL error with cl-smtp

This is a recent error that I can't find any documentation for. It might not be cl-smtp specific, but it occurs each time I attempt to evaluate

 (cl-smtp:send-email "localhost" "source@email.com" "test@email.com" "TEST" "Testing email from Common Lisp")

from the REPL. The error output is

debugger invoked on a SB-INT:SIMPLE-PROGRAM-ERROR in thread #<THREAD
                                                              "initial thread" RUNNING
                                                              {AAE38D1}>:
  invalid keyword argument: :SERVE-EVENTS (valid keys are :AUTO-CLOSE, :INPUT,
  :OUTPUT, :ELEMENT-TYPE, :EXTERNAL-FORMAT, :BUFFERING, :TIMEOUT).

Type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated 开发者_JS百科name):
  0: [ABORT] Exit debugger, returning to top level.

(SB-PCL::CHECK-APPLICABLE-KEYWORDS
 0
 (:AUTO-CLOSE :INPUT :OUTPUT :ELEMENT-TYPE :EXTERNAL-FORMAT :BUFFERING
  :TIMEOUT)
 -303677905
 10)
0] 0

I'm running Debian 6 with postfix and SBCL 1.0.40, and cl-smtp installed via quicklisp. Sending email through the telnet interface with the same source, server, target, subject and body (whether from the same unix user or with root) works fine. This setup also works fine (even from the REPL) on other machines that run the same software stack.

Can anyone see what I'm doing wrong?

That particular error is not coming from cl-smtp. Miscellany googling suggests that it's an internal API mimatch. Looking at the available flags, it seems as if it's a socket error( input, output, buffering, timeout).

SBCL 40 is almost a year old, SBCL 51 is fresh off the presses... I suggest upgrading!