After you install the security update 2507938 on a computer that is running the release version of Windows 7 or the release version of Windows Server 2008 R2, you may notice that Event ID 33 is logged in the event log.
This is a known issue and is documented in http://support.microsoft.com/kb/2507938 now
This update replaces C:\Windows\System32\conhost.exe with version 6.1.7600.16385 (14/07/2009) by 6.1.7600.16823 (2/06/2011) which causes the problems.
Work around this by applying one of the two below:
1. Apply KB977648, but please note that this would put the system on the QFE branch for this component, which means the system would be on the Hotfix branch and not the General Release branch.