Please check that you have not already scheduled this email to be sent out - as if so you will see that you have 'no recipients' to send your email out to as the emails will be 'Queued'. 

The screenshot below shows that there are no recipients to send out an email campaign to: 

On the day the email is scheduled to go out you will see on the Campaign Overview area inside the e-Marketing section the heading 'Queued' and next to this it will show you the number of emails queued to go out that day as shown below: