ntoskrnl.exe bad pool caller blue screen on win xp

had a xp pro machine that encounter the below blue screen error. what could be the causes of it?

Dump File         : Mini030211-01.dmp
Crash Time        : 3/2/2011 4:06:32 PM
Bug Check String  : BAD_POOL_CALLER
Bug Check Code    : 0x000000c2
Parameter 1       : 0x00000007
Parameter 2       : 0x00000cd4
Parameter 3       : 0x00001000
Parameter 4       : 0x8a94d008
Caused By Driver  : ntoskrnl.exe
Caused By Address : ntoskrnl.exe+22f43
File Description  : NT Kernel & System
Product Name      : Microsoft® Windows® Operating System
Company           : Microsoft Corporation
File Version      : 5.1.2600.6055 (xpsp_sp3_gdr.101209-1647)
Processor         : 32-bit
Full Path         : C:\WINDOWS\Minidump\Mini030211-01.dmp
Processors Count  : 4
Major Version     : 15
Minor Version     : 2600
Dump File Size    : 114,688