Something similar occured to me. Right after cpu_startnext() function started procnto:

System page at phys:84709000 user:84709000 kern:84709000
Starting next program at v84755bd4

Shutdown[0,0] S/C/F=5/4/3 C/D=84732850/84799c4c state(c0)= now lock
QNX Version 6.5.0 Release 2010/07/09-14:41:25EDT
shle context[84798378]:
0000: 00000000 fffffff8 847983f0 00000000 00000000 00005100 00000000 84700000
0020: 1ffffffe 847983d0 00004fe0 1fffffff 84799f18 84799f14 84798468 847983d0
0040: 400000f1 8474b820 84708000 00000000 000000d0 8474b782
instruction[8474b820] (pa@347):
03 a0 09 00 63 5f 79 84 5b 01 63 60 04 e2 2d 40 0c 70 d1 91 1c 35 01 76 2d 46
stack[847983d0]:
0000: 00000002 00000000 00000000 8470b000 84bfffff 00000000 00000000 84700000
0020: 84707fff 00000000 00000000 00000000 00000000 00000000 00000000 00000000
0040: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
0060: 00000000 00000000 00000000 84798440 8470926d 00000000 8474b758 84798468

Seems like there's no process started yet (no PID in kernel dump), addresses seem to be OK (things are where I loaded it
 using tftp), examining signal.h, sigininfo.h and fault.h gave me following S/C/F cause:
- S: SIGTRAP
- C: TRAP_CRASH (or NSIGTRAP)
- F: BREAKPOINT instr.

I have no clue why breakpoint instruction was reached. Image spec is like this:

[image=0x84720000]
[virtual=shle,binary] .bootstrap = {
  startup-mb442
  PATH=/proc/boot procnto
}

libc.so
[type=link] /usr/lib/ldqnx.so.2=/proc/boot/libc.so

[+script] .script = {
        display_msg Welcome to QNX Neutrino 6.5.0 on the mb442-derived board
        SYSNAME=nto
        TERM=qansi
        HOME=/
        LD_LIBRARY_PATH=.:/tmp/:/proc/boot:/usr/photon/lib:/dll:/lib:/lib/dll:/usr/lib:/usr/photon/dll:/opt/lib
        PATH=.:/tmp:/proc/boot:.:/sbin:/usr/sbin:/usr/bin:/bin:/usr/local/bin:/usr/photon/bin:/opt/bin
        [+session] ksh &
}

###########################################################################
## File system links
###########################################################################
[type=link] /bin/sh=/proc/boot/ksh
[type=link] /tmp=/dev/shmem

libcam.so.2
libm.so.2

###########################################################################
## QNX applications
###########################################################################
syslogd
ls
ksh
pipe
pidin
slogger
sloginfo
slay
mount
umount
cat
cp
rm
pipe
mkdir
kill
hogs
grep
chmod
sleep
tracelogger
shutdown
use

###########################################################################
## END OF BUILD SCRIPT
###########################################################################

As you can see, my welcome message wasn't displayed, kernel crashed earlier. I tried to change procnto to procnto-instr 
- no change, kernel dump is still the same. I placed plenty of kprintf in libstartup functions, all of them were 
displayed at boot time, so at least startup-mb442 seems to be OK. I feel not experienced enough to move further with 
this.