I am having this same problem and have changed the line in ~\Sitefinity\Admin\ControlTemplates\RssFeeds\ChannelsProvidersLayout.ascx
|<asp:Repeater ID="availableSources" runat="Server">
|<asp:Repeater ID="feedsInfo" runat="Server">
That is correct isn't it? I'm still getting the error calling for
|A required control was not found in the template for "". The control must be assignable form type "System.Web.UI.WebControls.Repeater" and must have ID "availableSources".
I have restarted the app pool and reset the web.config file - it's still looking for that repeater ID. We're using v3.7.