Cant restore stock rom in galaxy y and format failure I installed Hyperion custom ROM. Before installing it I made a complete backup. Then now I thought to switch back to my original OS − but it is saying some error like format failure, cant unmount system etc.

What could be the problem here?

Device name: Galaxy Y
Recovery tool: CWM
Custom ROM used: Hyperion

Error Report:
Checking MD5 sum
E:format_volume failed to unmount/system
error while formatting/ system
You can switch to stock ROM for Galaxy Y by using the latest version of Odin and downloading the stock ROM. You can find these files in other forums.