Form Validation max_length not working?

[eluser]Jacob Graf[/eluser]
I am trying to use max_length[10] for some fields with form_validation and I keep getting the following error upon page load. If I remove all of the max_length checks, everything works great!

Code:

A PHP Error was encountered

Severity: Warning

Message: mb_strlen() expects parameter 1 to be string, array given

Filename: libraries/Form_validation.php

Line Number: 982

Here is an example of one of my rules...

Code:

array (
      'field' => 'city',
      'label' => 'City',
      'rules' => 'required|max_length[30]'
      ),