I faced the same problem and was able to solve as follows:
The installation of KB3033929 seems to fail because on rebooting Windows expect that the boot partition will be the Windows one. However, when Grub is installed the boot flag (the bit that says which partition has the boot code) is not in the Windows boot partition.
You will then have to remove the boot flag from the Grub partition and attribute it to the Windows boot partition. This can be easily done following the process below:
- Go to gparted.org, download the live gparted CD/USB (http://gparted.org/livecd.php)
- Build the bootable CD or USB (instructions on doing this are on the site)
- Boot the PC with this CD/USB and start Gparted (if it was not already started)
- Determine which is the partition that contains Windows (the partition that should be booted next time)
- Select the one partition (click on it with mouse) at a time and click on menu item "Partition" and on it click on "Manage Flags". If the boot flag is checked, this is the partition from which the PC will boot (This means that Grub is installed in this partition). Take note of this partition. Uncheck the boot flag of this partition.
- Select the partition where Windows is installed, click on the "Partition" menu and in it click in the "Manage Flags" and put a check mark (mouse click) on the "boot" checkbox.
- Remove the CD/USB and reboot the PC, It should reboot directly in Windows. Then install the KB3033929 update. Reboot the PC to finish the update installation.
- Reinsert the CD/USB and reboot the PC into Gparted. Uncheck the boot flag in Windows partition and attribute it to the partition it was before you started.
- Reboot the PC. It is done.
There is a catch to this process. If Grub was installed in the MBR, you will need to reconstruct the original Windows MBR by using the Windows installation or recovery CD. Also, if installed in the MBR, the "Boot" checkbox may not be checked.
Should you run into problem, you may resort to "Parted Magic" (https://partedmagic.com/) and download their .ISO which has a lot of tools to help recover (it even offer Gparted).
You must be careful and make backups of your data before proceeding to follow the above process.