Comment 9 for bug 1091464

A second workaround, more convienent than the USB boot is to invoke the EFI device select menu, select HDD, then select ubuntu or Windows (both of which work). The ubuntu selection starts grub, but from grub, the Windows boot still fails with the above chainloader error.
  With the number of different brands mentioned in this bug, I begin to doubt the problem is vendor related. Maybe something we did caused this, so here's what I did:
  My first install was to a USB stick without ann EFI partition( used HD EFI, booted Ubuntu OK, did not boot Windows, and killed the Windows boot off the hard disk when not present). Installed to (prepared HD) in this condition, worked, but got a grub install error (Windows boot worked again). Installed to USB again after putting on a EFI partition, the install still mounted the HD EFI, which I manually unmounted and replaced with the USB EFI (this worked). At this point, the HD /EFI/ubuntu directory was corrupted, so had to manually delete it and replace the signed binaries. The USB would boot Ubuntu, but not Windows, and the HD would boot Windows (default). Using efibootmgr -v, I could see that the ubuntu boot was set up wrong, trying to boot grub instead of shim -- but much to my surprise, it still booted, so I surmise a silent failure, then a fallback to the /EFI/Boot/bootx64.efi (which was a copy of shim) which succeeded. I manually added (grub-install --uefi-secure-boot /dev/sda) a correct shim boot path, which worked too. I normally now enter F12 to select ubuntu or Windows. Not a totally clean history, but on the other hand, the machine has never been out of secure boot, I have never run boot-repair, and the only EFI variable manipulation I have done is through grub-install.