Hi Jamesbone, Thank you for your reply.
I found this probably be symlink setting problem in init.rc.
The setting in ~imx6/etc/init.rc is
mkdir /mnt/media_rw/udisk 0755 system system
symlink /mnt/media_rw/udisk /storage/udisk
And, In ~/device/fsl/PROJECT/init.rc the setting is
mkdir /storage/udisk 0000 system system
mkdir /mnt/media_rw/udisk 0666 system system
symlink /mnt/media_rw/udisk /udisk
If I comment both line in ~imx6/etc/init.rc, this error will not happen again
Any idea?