boot panic on current(04.20)

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  boot panic on current(2009.04.20).it seems caused by usbus4

Root mount waiting for: usbus4
uhub4: 8 ports with 8 removable, self powered
Root mount waiting for: usbus4
ugen4.2: <NEC> at usbus4
Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0x0
fault code              = supervisor read, page not present
instruction pointer     = 0x20:0xc08ed3a3
stack pointer           = 0x28:0xe4c38b40
frame pointer           = 0x28:0xe4c38b44
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0,pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 28 (usbus4)
trap number             = 12
panic: page fault
cpuid = 0
uptime: 5s
Cannot dump. Device not defined or unavailable.