bonita form

Access denied to the form.

I have created a web page that allow me to start a case. When the case has been started , it showing me a bonita form that contain a select field for selecting a user to assign task acording the work flow.

I have assigned a task to user , but when i'm trying to do it , it showing me this message:

Access denied: you do not have the rights to view this page.

How i can fix it?

Best regards!