Evaluating (global-set-key "\C-<" 'ding) in emacs buffer leads to a error invalid modifier in string

[Glauber Prado]

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and the precise symptoms of the bug:

the subject says it all, contact me for more info if needed be.

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In GNU Emacs 23.0.0.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.10.13)
of 2007-07-29 on gredesk
Windowing system distributor `The X.Org Foundation', version 11.0.10300000
configured using `configure  '--with-gtk' '--enable-font-backend' 
'--with-xft' '--with-png' '--with-gif' '--with-jpeg' '--with-tiff' 
'--with-xpm' '--with-x''

Important settings:
 value of $LC_ALL: pt_BR.UTF-8
 value of $LC_COLLATE: nil
 value of $LC_CTYPE: nil
 value of $LC_MESSAGES: nil
 value of $LC_MONETARY: nil
 value of $LC_NUMERIC: nil
 value of $LC_TIME: nil
 value of $LANG: pt_BR.UTF-8
 value of $XMODIFIERS: nil
 locale-coding-system: utf-8-unix
 default-enable-multibyte-characters: t

Major mode: Emacs-Lisp

Minor modes in effect:
 lazy-lock-mode: t
 highlight-tail-mode: t
 display-time-mode: t
 erc-list-mode: t
 erc-menu-mode: t
 erc-autojoin-mode: t
 erc-ring-mode: t
 erc-pcomplete-mode: t
 erc-track-mode: t
 erc-track-minor-mode: t
 erc-match-mode: t
 erc-button-mode: t
 erc-fill-mode: t
 erc-stamp-mode: t
 erc-netsplit-mode: t
 minibuffer-indicate-depth-mode: t
 icicle-mode: t
 shell-dirtrack-mode: t
 erc-smiley-mode: t
 erc-irccontrols-mode: t
 erc-noncommands-mode: t
 erc-readonly-mode: t
 tooltip-mode: t
 tool-bar-mode: t
 mouse-wheel-mode: t
 menu-bar-mode: t
 file-name-shadow-mode: t
 global-font-lock-mode: t
 font-lock-mode: t
 blink-cursor-mode: t
 global-auto-composition-mode: t
 auto-composition-mode: t
 auto-compression-mode: t
 line-number-mode: t

Recent input:
C-x C-e q M-x r e p o r <tab>
b <tab> <return>