In case you installed the .NET Framework 3.5.1 hotfix KB2844286 (security bulletin MS13-052) on a SharePoint 2010 environment and got an error message when using a WebPart, an updated hotfix package is now available.
You may receive the following exception while executing web parts in Microsoft SharePoint applications:
Error while executing web part: System.NullReferenceException: Object reference not set to an instance of an object.
at System.Xml.Xsl.XslCompiledTransform.Load(MethodInfo executeMethod, Byte[] queryData, Type[] earlyBoundTypes)
at Microsoft.Xslt.STransform.GetCompiledTransform()
at Microsoft.SharePoint.WebPartPages.BaseXsltListWebPart.LoadXslCompiledTransform(WSSXmlUrlResolver someXmlResolver)
at Microsoft.SharePoint.WebPartPages.DataFormWebPart.GetXslCompiledTransform()
at Microsoft.SharePoint.WebPartPages.DataFormWebPart.PrepareAndPerformTransform(Boolean bDeferExecuteTransform)
Please go to http://support.microsoft.com/kb/2872441 and install the updated hotfix package.
More information you can find also here: MS13-052: Description of the security update for the .NET Framework 3.5.1 on Windows 7 Service Pack 1 and Windows Server 2008 R2 Service Pack 1: July 9, 2013
It might be also recommended to install this re-released hotfix on all computers because this .NET feature XslCompiledTransform will be used by a lot of applications.