i Have seen this quite a few times.
I Have lots of errors like this:
[MissingWebPart] WebPart class [b2faa275-7008-740a-a014-0055b7420d15] (class [Microsoft.SharePoint.Portal.WebControls.SiteFeedWebPart] from assembly [Microsoft.SharePoint.Portal, Version=184.108.40.206, Culture=neutral, PublicKeyToken=xxxxx]) is referenced  times in the database [WSS_DBName], but is not installed on the current farm. Please install any feature/solution which contains this web part. One or more web parts are referenced in the database [WSS_DBName], but are not installed on the current farm. Please install any feature or solution which contains these web parts.
Here is a very handy site with a solution but did not work for me.
First Run this script in SQL Query Analyzer:
Change DB Name and the ID to the one's in the error message