Stack overflow before kernel load..

Hi,

Any ideas why the bootloader prints a 'error: stack overflow' message 
and request
user confirmation to load the kernel manually?

$ uname -a
FreeBSD marina.localdomain 8.2-PRERELEASE FreeBSD 8.2-PRERELEASE #1: Wed 
Feb 16 03:38:23 EST 2011     
root_at_:/usr/local/freebsd8/src/sys/amd64/compile/GENERIC.ndebug  amd64


Thanks,

Etienne