Reiner,
I'd appreciate it if you would try the following (Right now, you're the only one who is reliably producing this particular problem).  First, reinstall the 6.43 revision of gnus-sum.el.  Then apply this patch.
diff -r6.243 gnus-sum.el
11200c11200,11201
<      (all nil)
---
>      (all 
>       (setq older (gnus-uncompress-range older)))


Kevin

Reiner Steib wrote:
On Tue, Nov 26 2002, Kai Großjohann wrote:

  
Katsumi Yamaoka <yamaoka@jpl.org> writes:

    
While compiling Gnus CVS, the byte-compiler warns as follows:

While compiling gnus-summary-insert-old-articles in file [...]gnus-sum.el:
  ** gnus-range-difference called with 1 argument, but requires 2
Wrote /Work/gnus/lisp/gnus-sum.elc
      
[...]
  
Better now?
    

Sorry, not for me. When I call `/ o' I get the following backtrace:

,----[ `/ o' with revision 6.243 of gnus-sum.el ]
| Debugger entered--Lisp error: (wrong-type-argument
| number-or-marker-p (121011 . 121196))
|   gnus-sorted-difference(((121011 . 121196)) (121197 121198 121199))
|   gnus-summary-insert-articles(((121011 . 121196)))
|   gnus-summary-insert-old-articles(nil)
| * call-interactively(gnus-summary-insert-old-articles)
`----

When I replace `gnus-summary-insert-articles' and
`gnus-summary-insert-old-articles' with the versions from revision
6.238 (the one before the changes in the agent code) it works fine.

Bye, Reiner.