Install failed, rolled back.

Hi,

Few Clients notified from upgrading 12.1.6 MP4 (12.1.6867.6400) to MP5 (12.1.7004.6500) ''Install failed, rolled back''

Uninstalled the previous and tried to push the same upgrade pack - but failed.

Finally used Cleanwipe tool, then it took properly. 

Instead of using cleanwipe what could be the fault?

Thanks,