mobile

Hope someone can help me. I am using an AT & T sim on a Verizon Galaxy S5 SM-G900V. Works well for the most part. The one thing that won't work is the Mobile Hot Spot. No matter what I do, I get the message "Checking Subscription Status.....Unable to Connect...Mobile number not found." Any suggestions on how to make this work so I can connect to my laptop? Phone is not rooted....at least not yet if I can avoid it I'd like to, but if that's the only way.....Point me where I need to go. Thanks!