I kept getting this error message when I modify a list in SharePoint Designer 2010. I’m trying to modify a column and apply some conditional formatting. each time i do this, it looks fine in SPD, so I save and close. When I save and close I get the correlation ID errorm message. The other interesting thing is that this basically makes the view i’m working from unuseable. I’m also unable to make other basic changes in SPD to lists as I get the same problem.I looked up the log in ULS Viewer and it gave me the following:
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.SharePoint.WebPartPages.BaseXsltListWebPart.LoadXslCompiledTransform(WSSXmlUrlResolver someXmlResolver)
at Microsoft.SharePoint.WebPartPages.DataFormWebPart.PrepareAndPerformTransform(Boolean bDeferExecuteTransform)
Finally solved this by uninstalling this Windows KB2844286 did and then rebooted my machine. which then solved my issue