Playbook sim card issue

Hi

i got this playbook from a local store . It is from at&t , as soon as i inserted sim in mobile network it is showing like this "this phone has been blocked and cannot be used on the network (MM#6)".

What is this means , please let me know . Any way i can unlock it ?

Thanks
kiran

is it a tablet sim? I didnt think that any of the US carriers sold the LTE playbook. Are you sure its from ATT?

Probably stolen and reported is my guess. Can you return for full refund?

Q10 with Telus on 10.3.0.296