kgdb & vmcore Cannot access memory at 0x252d1

[dhaneshk k]

list,

 I  am new to kernel debugging,   I compiled  a new 
kernel with     options   KDB and DDB    in addition to the GENERIC
config and booted with the new  kernel.( Goal is to debug  the
coredumps  in my laptops /var/crash/vmcore  files and try to find and
fix the panic/situation which produce these coredumps)

I tried to analyze   all  of the   vmcore files    in my /var/crash/vmcore.x    core dumps

steps done
after booting  into the   new kernel

#  cd /usr/obj/usr/src/sys/MYCUSTORMKERNEL
#kgdb kernel.debug  /var/crash/vmcore.0

 kgdb kernel.debug /var/crash/vmcore.0
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This GDB was configured as "i386-marcel-freebsd"...
Cannot access memory at address 0x252d1
(kgdb) 
(kgdb) 

For
all the vmcore files  I am getting  this output..      Cannot access
memory at address 0x252d1,     how can I proceed  from here, 

How
to debug  what  is happening,  what makes the kernel  to dump these
vmcores  and  fix the issue by using  further debugging..
what  are the next steps ,  if there a message  in kgdb  "Cannot access memory at address   0x252d1 or any address"  

Please share your  suggestion and hints to debug  more from this point. I am stuck here..

Thanks in advance
Dhanesh