You may have left some information blank on your application. You must resolve this issue within 21 days of the first day of classes or you will have to go through a very lengthy petition process with the Registrar's Office.
Offers of admission are made only for the semester for which the student has applied. A student must request a deferral in writing to both their graduate unit and the Office of Graduate Studies no later than the Friday of the third week of classes of the semester of admission. A deferral is limited to one calendar year. After the one year deferral, a student must reapply. The Dean of Graduate Studies makes final approval for the requested deferral. More information can be found at www.unm.edu/grad/catalog/catalog04(2k6).html