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I get fatal error on all pages in Breadcrumb area

This error:

call to undefined function mb_strtolower()

means that mbstring extension is not enabled on your PHP. Please contact your web hosting provider and ask them to enable this extension on your PHP.

This extension should be enabled by default if you are using PHP 4.3.3 or newer.

For now, I would recommend to disable breadcrumb temporary while you are waiting for your hosting provider to enable this feature. To disable breadcrumb, please go to "Appearance > Theme Options > Header Options" then choose "Header: Banner Area" and in "Breadcrumb Visibility" choose "Hide".