If this occurs then the best thing to do is to duplicate your email campaign and then alter the subject line text.  Please follow the steps below:

1. Duplicate your email campaign by clicking on the Duplicate icon inside the Campaigns List window.

2. The duplicate template is then created you will find this at the top of your email campaigns list ready to edit.  

3. Click name of the email campaign to open up the Campaign Editor window - (please make sure you have clicked on the duplicated copy) 

4. Change the subject line in the Subject line field you see to the right of your email template:

5. Make sure you Save your changes by clicking on the Save button as shown in red above.

6. Please always send yourself a test of your duplicated email campaign and this should remove the problem. To do this click on the Send Test icon inside the e-Marketing campaigns window as shown below:

7. Enter your email address where you want the test to be sent to and click on OK to send.