I am having this issue, too, but think I am figuring it out. I bought my Verizon iPad3 at a Best Buy, and when I was there, the salesperson asked me if I was going to set up the Verizon month-to-month service, and I said yes. She said that she could do that for me while I was checking out. I said "can't I just do it from the iPad as soon as I leave the store?," and she responded "yeah, you could, but it will run on a different network, and won't be as fast." I questioned her, and she said that this is what their managers are telling them. At any rate, I let her activate the $30 2GB data for me.
Long story short, I realized this morning that I cannot access my Verizon acct (get error message) from my iPad, nor does the Personal Hotspot feature show up in my settings. I called Verizon, and they have just told me that the Best Buy salesperson signed me up for a CONTRACT, not a pre-pay, and that they also charged me a $35 activation fee. I had Verizon immediately cancel the contract, and that, in turn, made my SIM card no longer work. Verizon is now having me take my iPad to a local store where they will have to replace my SIM card, and hopefully I can get it working again.
To the original poster- did you activate your iPad data from the iPad, or did the store do it for you?