There are two common reasons for this.

The first is accidentally turning on the Typeface Embed ("On") parameter when a typeface has not been properly embedded. If you are trying to embed a typeface, see the Typography chapter of the SlideShowPro for Flash User Guide for instructions.

The second is applying a mask to the component on your FLA timeline. Flash doesn't allow dynamic text fields using system typefaces to be used underneath masks. The solution here is to either remove the mask, or embed a typeface for SlideShowPro for Flash to use in its text fields (see link above).