When you have a computer that has the High Precision Event Timer (HPET) hardware timer and Windows 8.1 installed, you encounter a 0x9F Stop error from the Usbhub.sys driver.
This issue occurs because both the HPET hardware timer and the hardware itself update certain registers at the same time, and this leads to a race condition.
To resolve this issue, install update rollup 2919394. For more information about how to obtain this update rollup package, click the following article number to go to the article in the Microsoft Knowledge Base:
2919394 Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 update rollup: February 2014
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates