You appear to have a very old version of pcl-cvs.
Which package version are you running?
>>>> "nbecker" == nbecker
<nbecker(a)fred.net> writes:
nbecker>
nbecker> `pcl-cvs-version' is a variable declared in Lisp.
nbecker> -- loaded from
"/usr/local/lib/xemacs/xemacs-packages/lisp/pcl-cvs/pcl-cvs.elc"
nbecker>
nbecker> Value: "1.05-CVS-$Name: $"
nbecker>
nbecker> `emacs-version' is a variable declared in Lisp.
nbecker> -- loaded from "/usr/local/src/xemacs-21.0-b57/lisp/version.el"
nbecker>
nbecker> Value: "21.0 \"Poitou\" XEmacs Lucid"
nbecker>
nbecker> Signaling: (wrong-type-argument stringp nil)
nbecker> expand-file-name(nil)
nbecker> find-file-noselect(nil)
nbecker> cvs-run-ediff-on-file-descriptor([[[... #1 ...] #0 (WRAPPER . ...)] [#0 [#1
... ...] (WRAPPER . ...)] (WRAPPER . [#<marker at 620 in *cvs* 0x8a2fe64> ...])])
nbecker> run-ediff-from-cvs-buffer(620)
nbecker> cvs-mode-ediff(620)
nbecker> call-interactively(cvs-mode-ediff)