I'm having the same problem. 

When my laptop is battery-powered after 10 minutes completely freeze. Seems to be related also with the wifi connection, as when not connected the computer doesn't hang. Currently using a Intel(R) Centrino(R) Wireless-N 1000 with windows 8.1 enterprise.

Sharing also a skydrive link with two zipped minidumps: http://sdrv.ms/1eGpcTM

Thanks in ad

GA

These were Related to vpnva64.sys Cisco AnyConnect VPN Client Virtual Miniport Adapter for Windows from Cisco Systems, Inc.  I would install the newest possible driver (yours is 2 years old)

Irp is active with 3 stacks 2 is current (= 0xffffe000104ddb08)
 No Mdl: No System Buffer: Thread 00000000:  Irp stack trace.  
     cmd  flg cl Device   File     Completion-Context
 [  0, 0]   0  0 00000000 00000000 00000000-00000000    

			Args: 00000000 00000000 00000000 00000000
>[ 16, 2]   0 e1 ffffe0000bfab050 00000000 fffff800b41d8054-ffffe0000fbbbc80 Success Error Cancel pending
	      Unable to load image \SystemRoot\system32\DRIVERS\vpnva64-6.sys, Win32 error 0n2
*** WARNING: Unable to verify timestamp for vpnva64-6.sys
*** ERROR: Module load completed but symbols could not be loaded for vpnva64-6.sys
 \Driver\vpnva	nt!PopSystemIrpCompletion
			Args: 00014400 00000000 00000004 

Thanks for the quick response, I will try and let you know.