BSOD Registry Error 0x51

Hi,

Im using a Fujitsu Lifebook E751 (Win7 Pro), I get the BSOD registry error quite often and the strange part is its just randomly.
Sometimes when I put in a usb or sometimes when im just working in any Office program.

Ive done a Hard disk check.
Tested both Ram sticks 1 at a time.
No results

Can someone look at the .dmp files?

Thanks in advance.

Code:

BugCheck 51, {1, fffff8a00081e010, 5425000, 374}

Probably caused by : ntkrnlmp.exe ( nt! ?? ::NNGAKEGL::`string'+9bda )

Code:

Usual causes:  Hardware failure, File system corruption, Security issues

Code:

0: kd> k
Child-SP          RetAddr           Call Site
fffff880`0c260788 fffff800`031ffc88 nt!KeBugCheckEx
fffff880`0c260790 fffff800`03168585 nt! ?? ::NNGAKEGL::`string'+0x9bda
fffff880`0c2607f0 fffff800`0316835c nt!HvMarkDirty+0x176
fffff880`0c260850 fffff800`032061a0 nt!HvMarkCellDirty+0x150
fffff880`0c2608a0 fffff800`0314f970 nt! ?? ::NNGAKEGL::`string'+0x11034
fffff880`0c2608e0 fffff800`0314ee54 nt!CmpMarkKeyDirty+0x16c
fffff880`0c260920 fffff800`0314ec54 nt!CmpFreeKeyByCell+0x44
fffff880`0c260960 fffff800`0314f495 nt!CmDeleteKey+0x250
fffff880`0c260a20 fffff800`02eca1d3 nt!NtDeleteKey+0x1f1
fffff880`0c260ae0 00000000`76fc1e7a nt!KiSystemServiceCopyEnd+0x13
00000000`025cd9d8 00000000`00000000 0x76fc1e7a

Marking something as Dirty, usually refers to the key/hive being accessed or written to. nt!CmDeleteKey was in the raw stack, means that the open key is deleted, although I couldn't see any routines referring to the handle being closed beforehand.

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