Your token is granted only for the permissions you specifically requested when you requested the the application be authorized by the user. To be able to post to a users wall, you need to ask the user to authorize the appropriate permissions.
Here is the facebook reference for requesting these permissions:
https://developers.facebook.com/docs/facebook-login/permissions/#adding
Depending on your app, you'll need to ask for either/both publish_actions
or publish_stream
when you get initial authentication from the user.