[Logician]

In register.php find:

if (strlen($username)<$minuserlength) {

before that add:

if (strlen($username)>XX) {
eval("standarderror(\"".gettemplate("error_toolong username")."\");");exit;
}

(Replace XX with max. char.number)

Login Admin CP/Create a New Template named error_toolongusername

Specify the text as you like (eg. "You user name is too long! Please go back and shorten it.")

Regards,