[imp] Warning: unknown encoding "BIG5" in /usr/local/apache/horde.beta/lib/String.php on line 155

[alex]

Hi all:
I am a Chinese user in Head,today i got warning message when opening mailbox 
folder:

Warning: unknown encoding "BIG5" in /usr/local/apache/horde.beta/lib/String.php 
on line 155

   or see http://webmail.thbuo.gov.tw/~txg16/string.jpg

I using php 4.2.2 --with-iconv --enable-mbstring
Here are my setting about mbstring in php.ini
[mbstring]
mbstring.internal_encoding = BIG5
;mbstring.http_input = auto
;mbstring.http_output = BIG5
;mbstring.detect_order = auto
;mbstring.substitute_character = none;
mbstring.func_overload = 7