Disallowed Key Characters

I have problem, when I add custom field to client like “IČO, DIČ, IČPDH” , slovak Tax informations, then go to edit client and press Save, got notification “Disallowed Key Characters.” . I’ve tried custom name without special chars “ICO, DIC, ICPDH” and same result.

Thanks for help.

Please take a look at http://www.snaver.net/2010/01/17/disallowed-key-characters-codeigniter-error/