Yeah, I just installed TWRP and responded affirmatively ("Yes" or "Accept") when the recovery asked me if I wanted it to root the device. I think this is a standard procedure if TWRP doesn't detect that the ROM is rooted; for me, I was asked just after I told it to reboot the phone.
its seems to be a root software problem . try with Quick Root V 4.1 tool may solve your problems. Download here : Quick Root V 4.1 - Download - 4shared