[Plugin: Custom sidebars] Forester Theme

Hi
I use the forester theme for an Italian Portal that is under construction.

To define custom sidebar per post/page/archive I tried to use the Custom Sidebar Plugin that I’ve used for other sites without problems.

But in this theme seems to have problem may be because it use pre defined sidebars. Lok here

When I go to a page with a custom sidebar deifined, the plugin section where I can choiche wath kind of Sidebar i can use tell me that there is no sidebar defined.

Do you have any solutions?
Thanks in advance
Fabrizio