Unable to refresh data for a data connection in the workbook. Try again or contact your system administrator. The following connections failed to refresh: PowerPivot Data

http://msdn.microsoft.com/en-us/library/ff487856.aspx

http://www.cjvandyk.com/blog/Articles/How%20do%20I%20-%20Install%20PowerPivot%20into%20an%20EXISTING%20SharePoint%202010%20farm.aspx


NOTE :- This feature is not available on SQL Server Standard Edition.

http://www.microsoft.com/sqlserver/en/us/product-info/compare.aspx