Unrecognized character sets?

Hiya all,

I am getting these warnings when processing emails with mhonarc
2.4.4 Is there a way i can fix this? Everythign seems to translate
okay but i still hate error messages. 

Thanks.. Mike

........................Warning: Unrecognized character set: gb2312
...Warning: Unrecognized character set: koi8-r
................................................................................
............................Warning: Unrecognized character set:
windows-1252
...Warning: Unrecognized character set: windows-1252
..Warning: Unrecognized character set: windows-1252
...................Warning: Unrecognized character set: windows-1252