Tethering not working !!Unlocked At&t phone but using it w/ T-Mobile

[Hugolara10]

I have an unlocked At&t Note 2 but I am currently using it with T-mobile, when I try to turn on the mobile hotspot it immediately turns off and tells me "Mobile Data is not available or Invalid SIM". My phone is currently running 4.3 Jelly Bean and I do not want to root it.