Server Crashes randomly

I have a problem, VM server 2008 R2 SP1 , running citrix is randomly crhasing, in event log I found following:

The computer has rebooted from a bugcheck. The bugcheck was: 0x0000003b (0x00000000c0000005, 0xfffff9600008744d, 0xfffff88007ba3de0, 0x0000000000000000)..

Any Idea what's causing it?
Here is results from debug:

here is info from Bugcehck: Bugcheck Analysis * * *

---

SYSTEM_SERVICE_EXCEPTION (3b) An exception happened while executing a system service routine. Arguments: Arg1: 00000000c0000005, Exception code that caused the bugcheck Arg2: fffff9600008744d, Address of the instruction which caused the bugcheck Arg3: fffff88007ba3de0, Address of the context record for the exception that caused the bugcheck Arg4: 0000000000000000, zero.

Debugging Details:

Page 125923 not present in the dump file. Type ".hh dbgerr004" for details

EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%08lx referenced memory at 0x%08lx. The memory could not be %s.

FAULTING_IP: win32k!xxxInternalInvalidate+7d fffff960`0008744d f6473208 test byte ptr [rdi+32h],8

CONTEXT: fffff88007ba3de0 -- (.cxr 0xfffff88007ba3de0) rax=0000000000000000 rbx=0000000000010485 rcx=0000000000000000 rdx=0000000000000b02 rsi=0000000000000000 rdi=0000000000000000 rip=fffff9600008744d rsp=fffff88007ba47c0 rbp=0000000000000000 r8=0000000000010485 r9=0000000000000000 r10=fffff900000004c0 r11=fffff900c26eac30 r12=0000000000000000 r13=0000000000000001 r14=0000000000000000 r15=0000000000000000 iopl=0 nv up ei pl zr na po nc cs=0010 ss=0018 ds=002b es=002b fs=0053 gs=002b efl=00010246 win32k!xxxInternalInvalidate+0x7d: fffff9600008744d f6473208 test byte ptr [rdi+32h],8 ds:002b:0000000000000032=?? Resetting default scope

DEFAULT_BUCKET_ID: WIN7_DRIVER_FAULT

BUGCHECK_STR: 0x3B

PROCESS_NAME: csrss.exe

CURRENT_IRQL: 0

LAST_CONTROL_TRANSFER: from fffff960001351a2 to fffff9600008744d

STACK_TEXT:
fffff88007ba47c0 fffff960001351a2 : 0000000000000000 0000000000000040 fffffa800678d330 0000000000000000 : win32k!xxxInternalInvalidate+0x7d fffff88007ba4840 fffff960001352a2 : fffffa800678d330 0000000000000000 fffff88007ba4ca0 fffffa8006109ab0 : win32k!xxxInternalUserChangeDisplaySettings+0x486 fffff88007ba4900 fffff960001330e3 : 0000000000000000 0000000000000000 fffff900c0f9ead0 fffff90000000040 : win32k!xxxUserChangeDisplaySettings+0x92 fffff88007ba49f0 fffff96000115cba : 0000000000000001 0000000000aff960 0000000000000000 ffffffffffffffff : win32k!xxxRemoteReconnect+0x6d7 fffff88007ba4bf0 fffff800016d9ed3 : fffffa8006f66b00 fffff88007ba4ca0 0000000000000000 0000000000000000 : win32k!NtUserCallOneParam+0x4e fffff88007ba4c20 000007fefd1b2aea : 0000000000000000 0000000000000000 0000000000000000 0000000000000000 : nt!KiSystemServiceCopyEnd+0x13 0000000000aff918 0000000000000000 : 0000000000000000 0000000000000000 0000000000000000 0000000000000000 : 0x000007fe`fd1b2aea

FOLLOWUP_IP: win32k!xxxInternalInvalidate+7d fffff960`0008744d f6473208 test byte ptr [rdi+32h],8

SYMBOL_STACK_INDEX: 0

SYMBOL_NAME: win32k!xxxInternalInvalidate+7d

FOLLOWUP_NAME: MachineOwner

MODULE_NAME: win32k

IMAGE_NAME: win32k.sys

DEBUG_FLR_IMAGE_TIMESTAMP: 50e64bda

STACK_COMMAND: .cxr 0xfffff88007ba3de0 ; kb

FAILURE_BUCKET_ID: X64_0x3B_win32k!xxxInternalInvalidate+7d

BUCKET_ID: X64_0x3B_win32k!xxxInternalInvalidate+7d

Followup: MachineOwner

You'll have to debug the dump file to determine what happened. My wild guess is on a driver causing bad pages. This post HOW TO: Debug Memory Dumps (Figure out what is causing a BSOD) is a pretty good step by step guid to using dumpchk to see what caused the BSOD