There's a known problem with Bluetooth connections...
MyWi OnDemand through Bluetooth hasn't worked since iOS 5.0. On 1/21 Intelliborn tweeted "We are working on a MyWi OnDemand update for 5.01". I'm hoping they can get a fix out soon.
It's not as convenient and uses more power, but creating a WiFi hotspot should still work for tethering your iPad.