Problem: Unable to save SharePoint Designer 2010 Data Source
Problem: Microsoft SharePoint Designer 2010 doesn’t allow you to add or edit a datasource, but also doesn’t list any existing Data Sources? This one had me for a moment, because the message was not very descriptive: “Unable to save Data Source”.
Be sure to check for any existing configuration files located in the ~site\_catalogs\fpdatasources directory. If there is a xml configuration file, but no corresponding datasource, delete the file and create it from scratch.