Can't boot Samsung galaxy ace GT-S5830i Failed to mount /system (Invalid argument)
There is a way to fix this. You have to sideload that ROM. For that -->


Just download adb (android debug bridge) minimum requirements. Sideload  your rom . It may seem to you that you got stuck there but don’t panic, wait at least 5 minutes. After that remove your battery and press (Power+Home+volume up) upto it shows samsung screen and then release. Then just install your rom from recovery mode.

No need to get panic on those failings. They happen sometime.