No language files defined in plans.config!

[Piuma]

Sometimes when I go to "next month >" or change calendar I receive
this error:
====================
Plans error:
No language files defined in plans.config!


Diagnostic information:
Script Name:plans.cgi

Plans version: 8.2.1
script name: plans.cgi
script file path: /var/www/html/plans_8.2.1/plans
script url path:

Theme url:
graphics url:
icons url:

Options:
default_template_path:
right_click_menus_enabled: 0
anonymous_events:
choose_themes:
====================

My system has Linux 2.6.30, apache 2.2.15, perl 5.10.0, I had search
the file "plans.config" but I don't have it.

Thanks in advance.