My phone is a moblie hot spot and I have no problems. I turn on the hot spot on the phone first then I turn on the nook and check the web settings to make sure the nook is picking up the phone, sometimes I have to tell the nook to connect with the phone wifi because it is picking up other wifi's that are in the area.
hope that helps
It has been reported that NOOK Color will not connect to ad-hoc networks. It wouldn't surprise me to find out that NOOK Tablet is the same.
If your phone is creating an ad-hoc network, this is probably your problem.