WinDbg Unresponsive After Crash

I am debugging a driver in a VirtualBox VM, with WinDbg attached to the target via COM port exposed to the host as a named pipe.

Debugging works fine - I can pause the target, set breakpoints, step through source files .etc

When my driver encounters a fatal error WinDbg dumps the following output to the console:

*** Fatal System Error: 0x00000050
                       (0xFFFFF88004126840,0x0000000000000001,0xFFFFF88003E12690,0x0000000000000000)

Driver at fault: 
***  MYDRIVER.sys - Address FFFFF88003E12690 base at FFFFF88003E12000, DateStamp 51249ae5
.
Break instruction exception - code 80000003 (first chance)

A fatal system error has occurred.
Debugger entered on first try; Bugcheck callbacks have not been invoked.

A fatal system error has occurred.

Connected to Windows 7 7601 x64 target at (Wed Feb 20 09:57:54.670 2013 (UTC + 0:00)), ptr64 TRUE
Loading Kernel Symbols
...............................................................
................................................................
..............
Loading User Symbols
.....
Loading unloaded module list
.....Unable to enumerate user-mode unloaded modules, Win32 error 0n30
Loading Wow64 Symbols
..........................................................
*******************************************************************************
*                                                                             *
*                        Bugcheck Analysis                                    *
*                                                                             *
*******************************************************************************

Use !analyze -v to get detailed debugging information.

BugCheck 50, {fffff88004126840, 1, fffff88003e12690, 0}

The little status box on the debugger command line is blank, and the debugger does not respond to the commands I type in.

I want to see the call stack and inspect the machine state, but the debugger remains unresponsive. Pressing BREAK/CONTINUE seems to have no effect.

I don't understand - what is the state of the debugger at this point?

I have a suspicion that my whole debugging setup is just very, very slow.

Debugging via com port is very slow, you must switch to virtualkd - http://virtualkd.sysprogs.org/ (its use shared memory between host and guest and much much faster). And don`t press anything while you waiting, its slow down process a little bit more. In general com is outdated and while debugging, without vm, all use firewire or usb interfaces.