Why system boots to grub rescue> prompt after a reboot ?

Issue

• The system boot process stops at a black & white screen with a grub rescue> prompt.
• Server is getting stuck at every reboot at the grub rescue> prompt.

• System fails to boot with "error: file 'grub2/i386-pc/normal.mod' not found"

  error: file 'grub/i386-pc/normal.mod' not found
  Entering rescue mode. . .
  grub rescue>
  

• System fails to boot with "error: file 'grub2/i386-pc/XYZ.mod' not found", where 'XYX' module could be one of the following: normal.mod net.mod priority_queue.mod bufio.mod datetime.mod boot.mod terminal.mod crypto.mod extcmd.mod getteext.mod