Hah! Finally! I'm not alone! I got this at least six times. In my case it appeared to only happen for E-mail coming from Lotus Notes mail users (how fitting). Here's a sample: Those mails received warning lines like, in the above case: Date: Thu, 16 Jul 1998 09:48:03 +0100 Gnus-Warning: This is a duplicate of message <80256643.002DF3A3.00(a)notes.teradyne.com&gt; Message-ID: <80256643.002DF3A3.00(a)notes.teradyne.com&gt; I finally went and tried to debug as follows: I had moved away a couple of files from ~/.gnus-crash-box to ~/.gnus-crash-box-<number> So I looked at the Backtrace and visited nnmail.el and gnus-util.el and did eval-buffer on them. I did an edebug-defun on the functions and the gnus-delete-line macro in the Backtrace. Now I moved back ~/.gnus-crash-box-1 to ~/.gnus-crash-box and did g runs the command gnus-group-get-new-news Quite to my surprise I was able to step through all the code and the mail was split correctly and the ~/.gnus-crash-box file was gone. I reproduced this for at least four more ~/.gnus-crash-box-<number> files. What is this, a Heissenbug? Best, Adrian Greg> in "21.0 \"Benadir\" XEmacs Lucid" with gnus-version=5.6.24 (xemacs Greg> 1.22) I get: Greg> Signaling: (invalid-function (macro . #<compiled-function (&optional n) "...(14)" [delete-region (progn (beginning-of-line) (point)) progn forward-line n 1 ((point))] 5>)) Greg> gnus-delete-line() Greg> nnmail-article-group(nnfolder-active-number) Greg> nnmail-check-duplication(&quot;&lt;199807231846.OAA03537(a)joule.ai.mit.edu&gt;&quot; nnfolder-save-mail nnfolder-active-number) Greg> nnmail-process-unix-mail-format(nnfolder-save-mail nnfolder-active-number) Greg> nnmail-split-incoming("~/.gnus-crash-box" nnfolder-save-mail nil nil nnfolder-active-number) Greg> nnmail-get-new-mail(nnfolder #<compiled-function nil "...(57)" [nnfolder-buffer-alist bufs buffer get-buffer buffer-name delq nnfolder-save-buffer kill-buffer nil] 4> "~/GNUSMail" nil) Greg> nnfolder-request-scan(nil "") Greg> gnus-request-scan(nil (nnfolder "")) Greg> gnus-read-active-file(nil t) Greg> gnus-setup-news(nil nil t) Greg> byte-code("..." [dont-connect did-connect gnus-group-quit gnus-run-hooks gnus-startup-hook gnus-make-newsrc-file gnus-startup-file gnus-current-startup-file gnus-slave gnus-use-dribble-file gnus-dribble-read-file gnus-use-grouplens bbb-login add-hook gnus-summary-mode-hook gnus-grouplens-mode gnus-setup-news nil level gnus-setup-news-hook gnus-start-draft-setup gnus-group-list-groups gnus-group-first-unread-group gnus-configure-windows group gnus-group-set-mode-line gnus-started-hook] 4) Greg> gnus-1(nil t nil) Greg> gnus(nil t nil) Greg> #<compiled-function (arg) "...(6)" [gnus arg t nil] 4 nil "P">(nil) Greg> call-interactively(#<compiled-function (arg) "...(6)" [gnus arg t nil] 4 nil "P">) -- Adrian Aichner Applications Engineer Teradyne GmbH Semiconductor Test Group Telephone +49/89/41861(0)-208 Dingolfinger Strasse 2 Fax +49/89/41861-217 D-81673 MUENCHEN E-mail aichner(a)ecf.teradyne.com