This issue occurs when the MBR of the bootable disk is damaged or altered.
To resolve this issue:
Boot the virtual machine using a Linux rescue CD or Linux live CD environment. Most rescue environments automatically mount the original filesystem under /mnt/sysimage.
Note: Some Examples of Live Linux CDs are:
Gentoo Live CD
Redhat rescue CD/DVD
Knoppix Live CD
PClinuxOS Live CD
Ubuntu Live CD
In the bash/rescue prompt, run this command to change root to the mounted installation:
chroot /mnt/sysimage
Navigate to /boot/grub.
Review the contents and ensure the grub.conf, menu.lst, stage1, stage2 files are available at this location.
Run this command to identify the disk and partition that is flagged as bootable:
fdisk -l
Typically, this would be /dev/sda1.
Run this command to reconfigure grub:
grub-install --recheck /dev/sda
This reinitializes grub in the MBR of disk /dev/sda.
After reconfiguring grub, unmount the rescue Linux CD and restart the virtual machine. The Linux operating system should now boot successfully to the grub menu to initiate the operating system boot up.
Additional Information
This issue may also occur if you have not selected the reconfigure option when a Linux operating system is converted from physical to virtual.