Powerpivot Sheet not working in sharepoint 2013

Hi,

When i try to open a poverpivot excel in sharepoint 2013, then on clicking on slicers/dicers i get the following error:

"We cannot locate a server to load the workbook Data Model."

Logs has the following entry:

05/15/2013 15:51:56.09  w3wp.exe (0x2448)                       0x05E8 SharePoint Server              Logging Correlation Data       xmnv Medium   Result=Id=NoStreamingServers; Microsoft.Office.Excel.Server.CalculationServer.SessionException: We cannot locate a server to load the workbook Data Model.     at Microsoft.Office.Excel.Server.CalculationServer.SessionWorkbook.HandleDataOperationException(Request request, DataOperation codeToRun)     at Microsoft.Office.Excel.Server.CalculationServer.SessionWorkbook.DoPivotInteractivity(Request request, Int32 externalSourceIndex, DataOperation dataOperation)     at Microsoft.Office.Excel.Server.CalculationServer.Operations.ApplySlicerSelectionOperation.StartExecution()     at Microsoft.Office.Excel.Server.CalculationServer.Operations.Operation.RunOperationAsync()     at Microsoft.Office.Excel.Server.CalculationServer.Operations.OperationSite.PrepareComplete(PrepareAsyncArgs args) 2b9e1b9c-a1cc-0016-6e83-095f19fbbe52

Please help. it's very urgent