The K2 Sidebar Manager (Sidebar Modules) has been deprecated and removed from K2 in r774 and the upcoming nightly build. If you are still using the K2 Sidebar Manager and you are planning to upgrade to the nightly builds/future stable releases, you have two options:
- Option A: Start using Widgets.
- Option B: Install the K2 Sidebar Manager plugin. Extract the zip into your wp-content/plugins/ folder and activate it via the Plugins admin. This is the same K2 Sidebar Manager that was included with K2 1.0-RC7, bugs and all. However, this plugin will also work with other widgets-ready themes. There is no support for this plugin.