Microsoft has recalled part of an update that was release earlier this week as part of April's Patch Tuesday. Microsoft discovered that in some cases users that had installed the update and had certain other third party installed may experience a blue screen with an Event ID 55 or a 0xc000021a Stop error after restarting. As a result Microsoft has pulled the part of MS12-036 that causes the problem and is asking users who may have already installed to the update to remove it.
Microsoft has published more information about how to remove the update here http://support.microsoft.com/kb/2839011 Microsoft is working on a fix for the problem update and should be able to push out a fix soon.