before release this firmware, I have tried to test usb function many times.
even launching official usb_mount script or testing original firmware, it is still unstable.
in GMenu2X, it only does the following command to mount usb as disk:
echo "/dev/mmcblk1p1" > /sys/devices/platform/musb_hdrc.0/gadget/gadget-lun1/file
so, maybe, you use another usb cable or via usb hub.
any suggestions are very welcome.