How can I trap and clean this recurring error?

[eluser]John_Betong[/eluser]
CodeIgniter 2.0

I use the email class and repeatedly get this log-file-error which is preventing users from sending emails:

Code:

ERROR - 2011-02-14 22:41:47 -->
  Severity: Notice  --> iconv()
  [<a href='function.iconv'>function.iconv</a>]:
  Detected an illegal character in input string
   /home/XXXXXX/YYYYY/ZZZZZ/CodeIgniter_2.0.0/system/core/Utf8.php 89