Boot failure - svn up from this morning

[AN]

Hi:

I'm having a major problem after updating a 12-current machine today. 
After buildworld/kernel/install cycle on reboot I'm getting the following 
failure:

"/boot/kernel/kernel text=0xb7716f data=0x100548+0x398358
elf64_loadimage: read failed
can't load file '/boot/kernel/kernel': input/output error
can't load file '/boot/kernel/kernel': input/output error

OK boot kernel.old
elf64_loadimage: read failed
can't load file '/boot/kernel.old/kernel': input/output error
can't load file '/boot/kernel.old/kernel': input/output error"

I have never experienced this failure before, and don't know how to 
proceed.  Any help recovering from this would be greatly appreciated. 
Thanks in advance.