This error is due to “corrupt boot”, you need to repair boot. Please follow below steps to fix this issue.
Step 1: Enable PPA
PPA is required in boot repair utility. Open terminal and run –
sudo add-apt-repository ppa:yannubuntu/boot-repair sudo apt update
Step 2: Install Boor Repair
sudo apt install boot-repair
Step 3: Run Boot Repair Utility
Click on Recommended repair
Click on Apply
Boot repair will prompt the result.
Restart computer and remove live pen drive or CD.
On the restart, you will be able to see the OS installed in the system. Boot your desired OS installed.