Why is my post showing in the 'Unscheduled' tab?

This may happen because of the following reasons:

• You may have added a post into the queue but you haven't specified time slots for that account. In such a case, you will need to go to 'Manage  Account' -> click on 'Edit' with the respective account -> and then 'Add' time slots.
• You may have scheduled more posts than your account limit.  These posts cannot be published and whence, have been moved to the 'unscheduled' tab.