lenovo k920 wont OTA after twrp, root, unlock

Lenovo K920 Pro lolipop
Hy

I have a lenovo K920 pro EU with the following software K920_S246_150520_row
I have unlocked bootloader, flashed TWRP 2.8... from xda, root.
Now i want to install K920_S271_150907_ROW and it not works.
I have unrooted, i have reset to factory and not updating.

I dont know , what i have to do, i tri to restore the factory recovery but i did find it!

Help pls

Thank u a lot.