Via Microsoft’s Community forums, there are a number of reports that people are experiencing the blue screen of death with a Stop 0x50 error following the install of August’s Windows Updates. The August updates were where Microsoft said they were going to incorporate Windows 8.1 Update 2 into the regular updates but this error is also affecting Windows 7 with reports of Windows Server 2008 R2 being affected as well. Only the 64-bit versions of the operating systems seem to be impacted by the update.
Three updates are related to the errors: KB2976897, KB2982791, and KB2970228. The kernel-mode driver updates are triggering the errors on some computers and the exact cause is unknown. Those updates add the ruble character as a currency marker.
Reverting the updates or restoring from a system restore point seems to allow the computers to boot again. In that same forum thread, a simpler solution is recommended:
I could solve it by booting from a DVD and removing the following file:
Microsoft Support is analyzing the problem and will release corrective updates according to a moderator in the thread. If you are experiencing these errors in your environment, I would recommend you pay attention to the growing Microsoft Community thread.
Update: Microsoft is recommending users uninstall KB2982791. https://technet.microsoft.com/en-us/library/security/MS14-045#ID0ENNAE