The Web server cannot connect to the specified data source because the query may contain errors, the data source may be unavailable ...

The Web server cannot connect to the specified data source because the query may contain errors, the data source may be unavailable or configured improperly, or your Web site is behind a proxy server or firewall.

If your Web site is behind a proxy server or firewall, verify that your server administrator has configured the Data Retrieval Services HTTP proxy server setting for Microsoft® SharePoint® Foundation.