BOOTMGR Missing Error after partition restoration

Hello All,

I just took an image of a laptop of 50GB C: drive partition.

Tried to restore C: drive partition of the Image on a machine with 30GB C: Drive. The machine restores successfully. But while booting it up it shows:

BOOTMGR Missing Press Ctr+Alt+Del to restart.

I then took another machine which had C: Drive of 40 GB and restore the same image on it. It restores successfully.

I then Shrinked the 40GB to 30GB and Tried restoring it. It also restores successfully.

Then what may be the problem in the first place??