number-or-marker-p

[Jim McCloskey <mcclosk@ling.ucsc.edu>]

In Emacs 20.7 running under Debian GNU/linux `testing' (kernel version
2.4.6), I have an intermittent but annoying problem.

Under two kinds of circumstance, I get the generic and mysterious
error-message:

   Wrong type argument: number-or-marker-p, (+ -4)

This happens (i) when I try to do filename completion with
                 `visit-file' or `dired'  
         or (ii) when I call `switch-to-buffer-in-another-frame' 
                 (C-x 5 b).

It happens only occasionally, though, and I can always fix it by
exiting the emacs session and restarting. I don't know how to
reproduce the behaviour reliably, but I can be sure that it will
happen ultimately if the emacs session is long enough.

Does anyone know how I might trace this problem to its origins? Or
solve it? Thanks very much in advance,

Jim