According to the minidump the avast! protection system is causing your problem.
I suggest removing avast! (which has been known to develop issues on some win 7 systems)
and replacing it with MSE
Virus, Spyware & Malware Protection | Microsoft Security Essentials
Which does not suffer from those issues.
Fault info:
aswSP.SYS Wed Feb 04 21:41:01 2009 (498A51BD) avast! Self Protection Driver
crash summary:
Code:
PAGE_FAULT_IN_NONPAGED_AREA (50)
Invalid system memory was referenced. This cannot be protected by try-except,
it must be protected by a Probe. Typically the address is just plain bad or it
is pointing at freed memory.
Arguments:
Arg1: fffffa8004c41d10, memory referenced.
Arg2: 0000000000000000, value 0 = read operation, 1 = write operation.
Arg3: fffff88002d6cfaf, If non-zero, the instruction address which referenced the bad memory
address.
Arg4: 0000000000000000, (reserved)
Debugging Details:
------------------
Could not read faulting driver name
READ_ADDRESS: GetPointerFromAddress: unable to read from fffff80002cfc100
fffffa8004c41d10
FAULTING_IP:
aswSP+afaf
fffff880`02d6cfaf 41f644241008 test byte ptr [r12+10h],8
MM_INTERNAL_CODE: 0
CUSTOMER_CRASH_COUNT: 1
DEFAULT_BUCKET_ID: VISTA_DRIVER_FAULT
BUGCHECK_STR: 0x50
PROCESS_NAME: AvastSvc.exe
CURRENT_IRQL: 0
TRAP_FRAME: fffff88003a4a720 -- (.trap 0xfffff88003a4a720)
NOTE: The trap frame does not contain all registers.
Some register values may be zeroed or incorrect.
rax=0000000000000000 rbx=0000000000000000 rcx=fffffa80071e4840
rdx=fffffa8006fde671 rsi=0000000000000000 rdi=0000000000000000
rip=fffff88002d6cfaf rsp=fffff88003a4a8b0 rbp=fffff88003a4aac8
r8=fffffa8006fde670 r9=0000000000000150 r10=fffff88002da6000
r11=fffffa8006b15900 r12=0000000000000000 r13=0000000000000000
r14=0000000000000000 r15=0000000000000000
iopl=0 nv up ei pl zr na po nc
aswSP+0xafaf:
fffff880`02d6cfaf 41f644241008 test byte ptr [r12+10h],8 ds:00000000`00000010=??
Resetting default scope
LAST_CONTROL_TRANSFER: from fffff80002a78a0c to fffff80002accd00
STACK_TEXT:
fffff880`03a4a5b8 fffff800`02a78a0c : 00000000`00000050 fffffa80`04c41d10 00000000`00000000 fffff880`03a4a720 : nt!KeBugCheckEx
fffff880`03a4a5c0 fffff800`02acae2e : 00000000`00000000 fffffa80`04c41d10 00000000`00000000 00000000`00000000 : nt! ?? ::FNODOBFM::`string'+0x4621f
fffff880`03a4a720 fffff880`02d6cfaf : fffff880`03a4a928 fffff800`00000001 fffff8a0`00000003 fffff800`00000000 : nt!KiPageFault+0x16e
fffff880`03a4a8b0 fffff880`03a4a928 : fffff800`00000001 fffff8a0`00000003 fffff800`00000000 fa8005b4`9b180400 : aswSP+0xafaf
fffff880`03a4a8b8 fffff800`00000001 : fffff8a0`00000003 fffff800`00000000 fa8005b4`9b180400 00000000`00000801 : 0xfffff880`03a4a928
fffff880`03a4a8c0 fffff8a0`00000003 : fffff800`00000000 fa8005b4`9b180400 00000000`00000801 00000000`00000000 : 0xfffff800`00000001
fffff880`03a4a8c8 fffff800`00000000 : fa8005b4`9b180400 00000000`00000801 00000000`00000000 fffff880`0104a19a : 0xfffff8a0`00000003
fffff880`03a4a8d0 fa8005b4`9b180400 : 00000000`00000801 00000000`00000000 fffff880`0104a19a fffffa80`04c41d00 : 0xfffff800`00000000
fffff880`03a4a8d8 00000000`00000801 : 00000000`00000000 fffff880`0104a19a fffffa80`04c41d00 00000000`00000000 : 0xfa8005b4`9b180400
fffff880`03a4a8e0 00000000`00000000 : fffff880`0104a19a fffffa80`04c41d00 00000000`00000000 fffff880`03a4ab30 : 0x801
STACK_COMMAND: kb
FOLLOWUP_IP:
aswSP+afaf
fffff880`02d6cfaf 41f644241008 test byte ptr [r12+10h],8
SYMBOL_STACK_INDEX: 3
SYMBOL_NAME: aswSP+afaf
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: aswSP
IMAGE_NAME: aswSP.SYS
DEBUG_FLR_IMAGE_TIMESTAMP: 4dc929b6
FAILURE_BUCKET_ID: X64_0x50_aswSP+afaf
BUCKET_ID: X64_0x50_aswSP+afaf
Followup: MachineOwner
---------