Dual boot with Windows 7 stopped working

I installed Ubuntu 16.04 LTS a few days ago on a brand new SSD, which was empty (sda), and kept the Windows 7 install which is on a separate SSD (sdb). Grub was installed properly (I guess on sda?) and after installing Ubuntu, I could select what system to start, from the grub menu. I tried that right after installation, and it did work fine.

But this morning, when I tried to restart Windows from the grub menu, I got the following error message:

error: no such device: 2844473F44470F4E.
Setting partition type to 0x7

Press any key to continue...

Now I cannot start my Windows system anymore. Any idea what has gone wrong, and how I could fix that?

Additional info that may help:

The initial fstab after Ubuntu install was:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda1 during installation
UUID=27e8f423-5046-4bf4-8bf6-3ca19a440e9c /               ext4    errors=remount-ro 0       1
# swap was on /dev/sda5 during installation
UUID=a123385a-2e28-45da-a699-574f26e43b54 none            swap    sw              0       0

which I changed (to add a network drive) into:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda1 during installation
UUID=27e8f423-5046-4bf4-8bf6-3ca19a440e9c /               ext4    errors=remount-ro 0       1
# swap was on /dev/sda5 during installation
UUID=a123385a-2e28-45da-a699-574f26e43b54 none            swap    sw              0       0
# added on october 25, 2016, following instructions @ http://ubuntuhandbook.org/index.php/2014/08/map-network-drive-onto-ubuntu-14-04/
//192.168.0.1/data                         /media/z        cifs    credentials=/home/jfs/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777   0       0

After trying boot-repair (see comments, it did not help so far), the report can be found at: http://paste2.org/AVeadskx