[9fans] multiboot archlinux and plan9 problem

[visof]

hello everyone
i have installed 9front on my laptop as native without any installation problem 
and then installed archlinux and multiboot them using grub2 from archlinux
, and i did menuentry for plan9 and it appears but when i choose plan9 from 
grub menu i got this error:
pbs..........ok
sectsize != 512
what is this mean? and how can i fix such error?
some info:
/dev/sda3