I am back with another Windows Update and SharePoint love story. This time, it involves a security update that will cause your web parts to give you the not so friendly “Unable to display this Web Part.” error.
If you check your Correlation ID, you will see an error similar to this:
[text]"Error while executing web part: System.NullReferenceException: Object reference not set to an instance of an object. at System.Xml.Xsl.XslCompiledTransform.Load…"[/text]
After looking at the logs, recent installed updates was the suspected issue. In this case, new .NET security updates stood out. A quick cross reference search across the standard forums indicated KB2844286 was the culprit (like in this thread http://tinyurl.com/ktjkzcq.)
People commenting on their Microsoft support tickets indicate the issues related to this KB are being evaluated. I am sure Microsoft will take the time to correct the issue rather than introduce more issues in a hasty patch fix. This does chalk up another reason to test your patches before you deploy to production.
The workaround is straightforward enough: remove the patch. A reboot was required for affected systems as IISRESET was insufficient after patch removal. If you are still installing updates automatically, consider hiding the update to avoid installing it again until the issues are resolved.