kernel trap 9 with interrupts disabled

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Hello!

My OS : 

4.8-STABLE FreeBSD 4.8-STABLE #0: Thu Sep  4 16:50:44 BST 2003 *@*:/usr/src/sys/compile/KRL7  i386

My machine is rebooting from time to time. Uptimes are not going more than 1 day. Without reason. After set :

dumpdev="/dev/ad0s1b"
dumpdir="/var/crash"

I've logs in /var/crash :

kernel.0 , vmcore.0

[root at box] (17:14) x /var/crash # tail vmcore.0
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled
kernel trap 9 with interrupts disabled

What can I do? any patch? please help me.