Arrow Connecting pen drive to moto g!!!!!!!!!!

I have a dual sim 16gb moto g bought 2 months ago. It is running kit Kat. I have not rooted my phone. Last week I bought an otg cable for connecting my pen drive to moto g. But whenever I connect it, phone is showing ' Damaged USB storage'
And in the notification area 'USB storage is damaged. Try formatting it'

When I try to format from moto g, phone will restart and nothing happens..
I have tried with 2 pen drives but same result. Both were in fat 32 and were working perfectly on pc..