[ubuntu] Booting with TAILS USB results in normal.mod not found on next Ubuntu boot

Hi,

I have a desktop with two HDDs, Win 10 on 500 GB and Ubuntu 16.04 LTS on a 80 GB HDD
I choose between the two at boot time by pressing F12 and choosing the appropriate disk

I just booted my system with TAILS from a USB pendrive and after shutdown tried booting Ubuntu but I get a normal.mod not found boot into grub_rescue
I Googled for a way out but ultimately had to reinstall 16.04 again.

Can someone please help and explain what is happening and how to prevent/mitigate this behavior?

Thanks in advance,
Tony