Originally Posted by id242
1) Are you allowing special characters in user names?
2) Did you just recently switch your database tables from ISO-8859-1 to UTF-8?

iconv has to do with multibyte characters. Does your new server have the iconv() library installed
https://www.hackersgarage.com/iconv-php-extension-installation-without-recompiling-php.html

I'll bet that's it. Thanks!