In recent CVS versions gnus-group-select-group (RET in the Group
buffer) gives me something like

        Symbol's function definition is void: nil

or a backtrace

,----
| Signaling: (void-function nil)
|   nil()
|   gnus-summary-highlight-line()
|   run-hooks(gnus-summary-highlight-line)
|   apply(run-hooks gnus-summary-highlight-line)
|   gnus-run-hooks(gnus-summary-update-hook)
|   gnus-summary-prepare-threads((("RE: HTTP proxy tunnel for SSH?" (... ...) (...)) ([414 "Talk: WEDNESDAY Nov. 20, 2002 on anonymous networking" "John Viega <viega@securesoftware.com>" "Sun, 10 Nov 2002 09:36:25 -0500" "<CA58416E-F4B9-11D6-A2AF-000393658EFC@securesoftware.com>" "" 4056 56 "nnmaildir sg-dc:414" ...])))
|   gnus-summary-prepare()
|   gnus-summary-read-group-1("nnmaildir:sg-dc" nil t nil nil nil)
|   gnus-summary-read-group("nnmaildir:sg-dc" nil t nil nil nil nil)
|   gnus-group-read-group(nil t)
|   gnus-group-select-group(nil)
|   call-interactively(gnus-group-select-group)
`----

Selecting any mail or news group gives similar results.  I have no
such trouble with an older CVS version.

,----[diff \*cvs-status\*-old \*cvs-status\*-new ]
| < Working directory: /home/jam/.xemacs/lisp/qgnus/lisp/
| ---
| > Working directory: /home/jam/.xemacs/lisp/pgnus/lisp/
| 10c10
| < 6.1697        Need-Update 6.1675      ChangeLog
| ---
| >               Up-To-Date  6.1697      ChangeLog
| 23,24c23,24
| < 6.102         Need-Update 6.96        gnus-agent.el
| < 6.254         Need-Update 6.253       gnus-art.el
| ---
| >               Up-To-Date  6.102       gnus-agent.el
| >               Up-To-Date  6.254       gnus-art.el
| 52c52
| < 6.13          Need-Update 6.12        gnus-range.el
| ---
| >               Up-To-Date  6.13        gnus-range.el
| 60,61c60,61
| < 6.53          Need-Update 6.52        gnus-start.el
| < 6.246         Need-Update 6.235       gnus-sum.el
| ---
| >               Up-To-Date  6.53        gnus-start.el
| >               Up-To-Date  6.246       gnus-sum.el
| 65c65
| < 6.20          Need-Update 6.16        gnus-uu.el
| ---
| >               Up-To-Date  6.20        gnus-uu.el
| 119c119
| < 6.32          Need-Update 6.31        nnrss.el
| ---
| >               Up-To-Date  6.32        nnrss.el
| 151c151
| < 6.24          Need-Update 6.22        spam.el
| ---
| >               Up-To-Date  6.24        spam.el
`----

Here is the body of the message generated by C-c C-b in the recent cvs

,----
| Oort Gnus v0.08
| XEmacs 21.4 (patch 8) "Honest Recruiter" [Lucid] (i386-debian-linux) of Tue Aug  6 2002 on eeyore
| 200 quimby.gnus.org InterNetNews NNRP server INN 2.2.2 13-Dec-1999 ready (posting ok).
| 
| 
| 
| 
| 
|