Hi I'm using a xslt based dataview webpart the steps i have taken to create a data view webpart is that 1. added a list view webpart on the page 2. Modified the toolbar property to show fulll toolbar 3. open the web page containing above list view webpart in sharepoint desginer and converted it to xslt based webpart (to make further changes in UI) 4. saved the page and previewed in browser

in browser web part was throwing the error while i was able to see it properly in desginer witout any error the error maesseged shown in webpart was:

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Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Windows SharePoint Services-compatible HTML editor such as Microsoft Office SharePoint Designer. If the problem persists, contact your Web server administrator.

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the error message provided in sharepoint log file was :

05/12/2010 17:56:29.54 w3wp.exe (0x19FC) 0x1E9C Windows SharePoint Services Web Parts 89a1 Monitorable Error while executing web part: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.SharePoint.WebPartPages.DataFormWebPart.ResolveParameterValuesToXsl(ArgumentClassWrapper argList) at Microsoft.SharePoint.WebPartPages.DataFormWebPart.PrepareAndPerformTransform()
05/12/2010 17:56:29.62 w3wp.exe (0x19FC) 0x1E9C Windows SharePoint Services Web Controls 88wy Medium SPDataSourceView.ExecuteSelect() - selectArguments: IsEmpty=True, MaximumRows=0, RetrieveTotalRowCount=False, SortExpression=, StartRowIndex=0, TotalRowCount=-1
05/12/2010 17:56:29.62 w3wp.exe (0x19FC) 0x1E9C Windows SharePoint Services Web Controls 88x2 Medium SPDataSourceView.ExecuteSelect() - formattedQuery = 1
05/12/2010 17:56:29.64 w3wp.exe (0x19FC) 0x1E9C Windows SharePoint Services Web Parts 89a1 Monitorable Error while executing web part: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.SharePoint.WebPartPages.DataFormWebPart.ResolveParameterValuesToXsl(ArgumentClassWrapper argList) at Microsoft.SharePoint.WebPartPages.DataFormWebPart.PrepareAndPerformTransform()