So this is a error which some of you might have definately faced while working with Android, flashing custom ROMs. The first and the most important step while using a custom ROM for me is to take the Nandroid backup via CWM , incase the ROM i am flashing soft-bricks the phone, I always have the backup !
But sometimes while working with backup, the restoration isnt as clean as we want, The CWM tries to restore the images only if the md5 sum is matched and this leads to a new problem what if the .md5 sum was deleted or md5 mismatch occurs? Obviously if that occurs you wont be able to restore the backup !
Here it is :
Boot the device (Connect the device – via adb , not in media storage mode) and do the following in CMD / Terminal
adb shell # cd /sdcard/clockworkmod/backup/2012-10-10.20.22.53 (Here 2012-10-10.20.22.53 is timestamp at which backup was generated, yours might be different! ) # rm nandroid.md5 # md5sum *img > nandroid.md5
Thats it ! that removes the existing md5 sum (which gave a mismatch in CWM) and generates a new one !
Try restoring the Backup now, it will be done in first attempt :)