Server Crash!

We have a 4-way smp linux box, running RedHat 5.1, with all kernel 2.2
patches, and running kernel 2.2.6 and squid 2.2.stable.3, 4 ultra-wide scsi
disks. This morning system was down hard, only error is in
/var/log/messages:

Aug 24 06:25:03 cache kernel: Unable to handle kernel NULL pointer
dereference at virtual address 00000000
Aug 24 06:25:03 cache kernel: current->tss.cr3 = 16eef000, `r3 = 16eef000
Aug 24 06:25:03 cache kernel: *pde = 00000000
Aug 24 06:25:03 cache kernel: Oops: 0000
Aug 24 06:25:03 cache kernel: CPU: 3
Aug 24 06:25:03 cache kernel: EIP: 0010:[<c016d662>]
Aug 24 06:25:03 cache kernel: EFLAGS: 00010202
Aug 24 06:25:03 cache kernel: eax: 0000018f ebx: d3bca2c0 ecx: c0230b8f
edx: 00000000
Aug 24 06:25:03 cache kernel: esi: d3bca2f0 edi: c0b530e0 ebp: d3bca370
esp: d6e65e68
Aug 24 06:25:03 cache kernel: ds: 0018 es: 0018 ss: 0018
Aug 24 06:25:03 cache kernel: Process squid (pid: 455, process nr: 48,
stackpage=d6e65000)
Aug 24 06:25:03 cache kernel: Stack: c016c5d2 d3bca2c0 c0b530e0 d3bca370
d3bca2c0 00000000 000005b4 00000001
Aug 24 06:25:03 cache kernel: d3bca480 cd311000 c016defe d3bca2c0
c0b530e0 000005dc d3bca2c0 00000010
Aug 24 06:25:03 cache kernel: d6e65f14 ce624c4c 232190c1 00000000
d6e65ec8 232190c1 d6e65f14 d3bca370
Aug 24 06:25:03 cache kernel: Call Trace: [<c016c5d2>] [<c016defe>]
[<c0174bdd>] [<c015879b>] [<c0157eca>] [<c01592ac>]
[<c0108c00>]
Aug 24 06:25:03 cache kernel: [<c010002b>]
Aug 24 06:25:03 cache kernel: Code: 66 39 0a 74 09 90 8b 52 04 66 39 0a 75
f8 83 7a 08 00 75 1e
Aug 24 06:25:03 cache init: Switching to runlevel: 6

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No previous error messages seemed to relate..
Any help would be great, I am willing to provide more information.
jen