I have just found an earlier thread that contained the answer. Here it is for anyone else who is may have this problem:

The Ballon Text style in your document has been modified so it is size 1 point. To change it in Word 2003:

1. Click the Styles and Formatting button on the Formatting toolbar.
2. In the bottom of the task pane, use the drop-down to choose Custom
3. Check the box for Balloon Text and click OK.
4. You should now be able to see Balloon Text in the task pane.
5. Right-click on it and choose Modify,
6. Change the font size and click OK.