Came in today to find the following error message showing up on seemingly random web parts and lists throughout our SharePoint 2010 Foundation farm. ULS Logs on the servers weren’t very helpful.
[This issue has been RESOLVED see updates below]

For the sake of search indexing, here is the text version of the error we are getting.
Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor such as Microsoft SharePoint Designer. If the problem persists, contact your Web server administrator.
We quickly tracked it down to a Security Update that was applied to our web front end servers last night. Check the OS below to find the KB update associated with your server.
Windows XP and Windows Server 2003
Windows 7 Service Pack 1 and Windows Server 2008 R2 Service Pack 1
Windows Vista Service Pack 2 and Windows Server 2008 Service Pack 2
This is in regard to the following Microsoft Security Bulletin for July 2013
As a temporary workaround, we found uninstalling the update (KB2844286) from your servers (all WFE’s and App servers) then performing an IISReset on the servers will resolve the issue. Several others have experienced this issue as noted in just one of many forums such as the one below
http://social.technet.microsoft.com/Forums/sharepoint/en-US/cc9a557b-93cd-40d5-965c-e0a2f107624d/unable-to-display-this-web-part-error-message-after-patch-kb2844286
If I find there is a solution better than uninstalling I will update this post to reflect that. As of right now, uninstalling this update is the best option.
[Update 7/16/2013 3:40pm]
It appears the error typically appears when a list or web part view has had the XSLT customized. At least in our Farm, that has been the common behavior.
[Update 7/17/2013 10:03am]
Not much of an update, but I’m awaiting contact from our Microsoft TAM to see about this issue. If we don’t hear from them soon, then we’ll be opening a ticket with Microsoft. Luckily we were able to work around the issue by uninstalling.
[Update 7/17/2013 12:50pm]
I just received confirmation from our TAM that Microsoft is aware of 2 issues regarding the patch noted in this article above. One of which appears to be the SharePoint issue we’re having.
[Update 7/17/2013 2:43pm]
Just spoke with our Microsoft Sr. Support Escalation Engineer assigned to our premier support ticket and here is their response (summarized).
“Our product group is currently working on the updated patch. We have no ETA for the new release at the moment.”
Looks like we wait then for a resolution.
[Update 7/17/2013 2:59pm]
One more confirmation from Microsoft Support and a link to the forum MS is using to track the issue publicly. No public information just yet beyond that, however.
“Both the SharePoint and .NET product groups are aware of the issue and they are in the process of fixing the patch.”
Follow the issue at this TechNet Forum
[Update 7/18/2013 9:24am]
So far I have heard of no updated patch being released yet by Microsoft. There were two MS Security Bulletin updates but it doesn’t appear they were related to this issue as they were for Bulletin MS12-006 and MS12-052.
[Update 7/21/2013 12:36pm]
Still no updated patch. Received an e-mail from our MS Support representative and they indicated they too have no ETA on any updates to the security patch. I guess I’d rather they take their time then rush an update out all to break something else. It would be a good idea if Microsoft were to either add a note to the update download page indicating the issue, or just pull the update altogether.
[Update 7/24/2013 8:28am]
I just got a message from our Microsoft Support representative and she informed me there is no update as of yet on a new download for the patch. No surprise there.
[Update 7/25/2013 7:50am]
As you can see from the comments that have arrived thus far, it appears Microsoft has provided a fix to the KB2844286 issue. We are in the process of testing it out in our DEV environment now. Let’s hope it fixes it and doesn’t cause more issues.
[Update 7/25/2013 8:22am]
I am at this point, comfortable with counting this issue RESOLVED. We’ve tested it in DEV and the solution resolves the problem and doesn’t seem to break anything else. We won’t be able to complete the resolution in our Production environment until after hours as we will have to re-install KB2844286 which will require a reboot and the patch requires at the very least an IISRESET.
Go to http://support.microsoft.com/kb/2872441 to download the update. Note: You will need to run an IISRESET for the update to take effect after installing.
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