I resolved the problem , as it written in wiki ubuntu

Error 11: Unrecognized device string...
* press any key to continue
* highlight "Chainload into GRUB 2"
* press e
* highlight "root xxxxxxxxxxxxxxxxxxxx"
* press e
* change "root xxxxxxxxxxxxxxxx" to "uuid xxxxxxxxxxxxxxxxxx"
* press b to boot "uuid xxxxxxxxxxxxxxxxxxx"
* load your kernel and press enterand after i entered to ubuntu , in terminal i
entered the following
sudo upgrade-from-grub-legacy
and every thing is ok know