grub2 - Problem to get inside Another OS (Windows 7)

I have intalled Ubuntu and Windows 7 in my laptop. When I select Windows 7 loader, this screen appears:

BOOTMGR is missing 

Press Ctrl+Alt+Del to restart.

But my ubuntu works fine.I then update the grub there I got the message:

Generating grub.cfg
Found linux image: /boot/vmlinuz-3.5.0-17-generic
Found memtest86+ image: /boot/memtest86+.bin
grub-probe : error filesystem
Found Windows 7 (loader) on dev/sda5
done

But can't access Windows 7 yet
what to do now ?