.net Application hanging. Weird crash-dump

A production server has an application running 24x7, and sometimes it starts consuming near 50% of CPU. I couldn't reproduce it locally, but I did a Memory Dump with adplus. The server has Windows 2008 Server 64bits, .NET 3.5. The application listens to a MSMQ and has a thread pool to execute operations, when I did the memory dump it was supposed to be running nothing, but it was still consuming CPU.

Below is the Dump. Do you know what can be happening?? It's weird that the slow thread also says GC Disabled! What's that?

It's weird I've an ASP.NET app in the same server and sometimes happens the same thing.

0:000> !threads
ThreadCount: 23
UnstartedThread: 0
BackgroundThread: 6
PendingThread: 0
DeadThread: 5
Hosted Runtime: no
                                              PreEmptive                                                Lock
       ID OSID        ThreadOBJ     State   GC     GC Alloc Context                  Domain           Count APT Exception
   0    1 1ec0 0000000000249c10      a020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
   2    2  84c 0000000000253470      b220 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA (Finalizer)
   3    3 10b8 0000000019d0f900    80a220 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA (Threadpool Completion Port)
   5    4 2184 0000000019d4a550   880b220 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA (Threadpool Completion Port)
   6    6 14a0 0000000019d602a0   180b220 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA (Threadpool Worker)
   8    7  490 0000000019d7db70   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
   9    8 2164 0000000019dae680   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  10    9  ac0 0000000019db4740   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  11    a 24cc 0000000019db51f0   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  12    b 1fb4 0000000019db5ca0   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  13    c 2408 0000000019db1520   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  14    d 1b44 0000000019db1fd0   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  15    e 1280 0000000019db2a80   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  16    f 206c 0000000019db8780   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  17   10 1ff8 0000000019db9230   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  18   11 2548 0000000019dc2120   200b020 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA
  20   18 2588 0000000019dc49d0   180b220 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 MTA (Threadpool Worker)
  21   1a 20a0 0000000019dc5570      b220 Disabled 0000000001653d88:0000000001655978 00000000002410b0     1 MTA
XXXX   26    0 0000000019dc89c0      9820 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 Ukn
XXXX   2c    0 0000000019dc5b40      9820 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 Ukn
XXXX   2b    0 0000000019dc3290      9820 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 Ukn
XXXX    5    0 0000000019dc8f90      9820 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 Ukn
XXXX   27    0 0000000019dc7850      9820 Enabled  0000000000000000:0000000000000000 00000000002410b0     0 Ukn

 0:000> !runaway
 User Mode Time
  Thread       Time
  **21:20a0      0 days 0:27:21.718**
   6:14a0      0 days 0:00:01.921
  18:2548      0 days 0:00:01.015
   2:84c       0 days 0:00:00.890
   (18 more....)

0:000> ~21s
*** WARNING: Unable to verify checksum for System.ni.dll
mscorwks!JIT_WriteBarrier_Fast+0x3:
000007fe`f88de5c3 4881fa607f4701  cmp     rdx,1477F60h

0:021> !clrstack
OS Thread Id: 0x20a0 (21)
*** WARNING: Unable to verify checksum for mscorlib.ni.dll
Child-SP         RetAddr          Call Site
000000001b05f090 000007fef651b1ba System.Net.TimerThread+TimerNode..ctor(Callback, System.Object, Int32, System.Object)
000000001b05f0d0 000007fef69a0c3f System.Net.TimerThread+TimerQueue.CreateTimer(Callback, System.Object)
000000001b05f180 000007fef651b73e System.Net.ConnectionPool.CleanupCallbackWrapper(Timer, Int32, System.Object)
000000001b05f1d0 000007fef651b560 System.Net.TimerThread+TimerNode.Fire()
000000001b05f2a0 000007fef64e6388 System.Net.TimerThread+TimerQueue.Fire(Int32 ByRef)
000000001b05f330 000007fef271175b System.Net.TimerThread.ThreadProc()
000000001b05f400 000007fef27a95fd System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
000000001b05f450 000007fef88e1552 System.Threading.ThreadHelper.ThreadStart()
0:021> kb
RetAddr           : Args to Child      : Call Site
000007fe`f6a1b87e : 00000000 (Edited) : mscorwks!JIT_WriteBarrier_Fast+0x3
000007fe`f651b1ba : 00000000 (Edited) : System_ni+0x70b87e
000007fe`f69a0c3f : 00000000 (Edited) : System_ni+0x20b1ba
000007fe`f651b73e : 000007fe (Edited) : System_ni+0x690c3f
000007fe`f651b560 : 00000000 (Edited) : System_ni+0x20b73e
000007fe`f64e6388 : 00000000 (Edited) : System_ni+0x20b560
000007fe`f271175b : 00000000 (Edited) : System_ni+0x1d6388
000007fe`f27a95fd : 00000000 (Edited) : mscorlib_ni+0x2f175b
000007fe`f88e1552 : 00000000 (Edited) : mscorlib_ni+0x3895fd
000007fe`f877e5e3 : 00000000 (Edited) : mscorwks!CallDescrWorker+0x82
000007fe`f878c83f : 00000000 (Edited) : mscorwks!CallDescrWorkerWithHandler+0xd3
000007fe`f887ae8d : 00000000 (Edited) : mscorwks!MethodDesc::CallDescr+0x24f
000007fe`f8839374 : 00000000 (Edited) : mscorwks!ThreadNative::KickOffThread_Worker+0x191
000007fe`f8732045 : 00000000 (Edited) : mscorwks!TypeHandle::GetParent+0x5c
000007fe`f8846139 : 00000000 (Edited) : mscorwks!SVR::gc_heap::make_heap_segment+0x155
000007fe`f8700e15 : 00000000 (Edited) : mscorwks!ZapStubPrecode::GetType+0x39
000007fe`f8700ae7 : 00000000 (Edited) : mscorwks!ThreadNative::KickOffThread+0x401
000007fe`f88614fc : 00000002 (Edited) : mscorwks!ThreadNative::KickOffThread+0xd3
00000000`76bdbe3d : 00000000 (Edited) : mscorwks!Thread::intermediateThreadProc+0x78
00000000`76d16a51 : 00000000 (Edited) : kernel32!BaseThreadInitThunk+0xd

I'm by far no expert here, but some more information that might be useful:

According to this, GC threads are created on CLR startup, at least for server GC, so not having enough threads for a GC run is possibly not even possible ;-)
The "Disabled" in the "GC" column of thread 21 just means that it decided to not be preemted by an eventual GC operation. This happends when the code on thread decides that it is doing a critical operation that should not be disturbed by a GC (like loading and assembly, hence fusion).
From the "kb" command output I would guess that you are actually using the server GC (stackframe "mscorwks!SVR::gc_heap::make_heap_segment"; workstation GC would have something with the class/namespace "WKS"). This is not unexpected as it should be the default on a "server operating" system. You should make sure about this using the "!eeversion" command. Additionally you should find out how many cores you have, because if the server GC runs,
it will use as many threads (one per logical/physical core).

Could it be, that the timer is firing pretty often, or faster than the previous one is finished. You can get an overview of threadpool thread usage using the "!ThreadPool" command.

Also, you might want to check the actual arguments to the methods and locals (!clrstack -a) and/or the current objects on the stack (!dso). Maybe that can shed some more light.

As wild guess, some googling for "System.Net.ConnectionPool.CleanupCallbackWrapper" yield the following links, maybe that could be your problem?