unable to mount system on twrp recovery samsung core i8262

I have rooted my phone and installed custom recovery ( twrp 2.7.1 )

Then i have backed up my data ,system,boot,cach……

And try to install any rom like cosmic rom,kitkat rom,lollipop rom or any rom or any system file like trying to deaodex my stock rom

I wipe cach and data and dalivd cach then tap install from sd card

Everything goes well but its finshed quickly and at the end it give me this

E:/unable to mount system

And its give me successful
But when i reboot system its still on samsung galaxy core i8262 screen
And nothing else

I went to recovery mode agine and a restore my backup and its work fine

Can any one help me please to slove this proplem
……. .