Please ensure that your code is being entered correctly. A common issue is the confusion of certain characters. We tend to see capital "I's" as in Iowa confused with lowercase "l's" like leopard and/or the number "1".
Our access codes do not contain lowercase "l's" (leopard) or the number "1"; in these cases, please use a capital "I" (Iowa).
Another reason may be that you have a used textbook and the code is no longer valid. You can purchase course only access on The MIT Press.
If none of these examples represent you, please submit a ticket with a picture of your access code and we will further investigate the matter.
