It looks like CoBlocks 2.23.0 plug-in is causing grief for widgets with the BeTheme. With COBlocks activated, the widget area throws an error and can't be edited.
Sorry, but we did not test this plugin with the theme. Our policy states that we do not support third-party plugins or custom code, so, unfortunately, we cannot help you.
Also, we cannot recommend any plugins other than the ones we support. You can find the list on this page, in the sidebar: