If the dreamer saw a blackboard in his dream, it signifies forgotten ideas even debts. If you look deeper into your past, you may find unsolved problems which you left behind. For all of us the blackboard reminds the childhood and the school, where you spent big time of your life and became an adult. The doubts and questions you had reflects at this time of your life. Make sure you have no hidden thoughts and/or emotions otherwise you will not be able to move on. The main explanation of this dream says that you have the debts, which must be solved.
Read more about dreaming of Blackboard in other dream meanings interpretations.