Why are you exporting as a SWF file from After Effects? This is almost always a bad idea. Tell us what you are trying to accomplish, and we can help you to find a better way.
I need to export into a .SWF file because, I need it for a school project.
In our project we are designing a E-newsletter for our IT project; in order to embed my animated banner (my after effects composition), I need to import it as .SWF because, the web designing software we are using for this project (Serif Webplus X6). Yes, I can export into other formats but it is then not possible for me to loop the animated banner in the E-newsletter as the web designing software isn't compatible with this feature. Therefore, I have to export it as .SWF to import it in the software and keep it looping.
It is nearly always a better idea to export your After Effects composition as a video file through Adobe Media Encoder and embed/link that video file within an SWF using Flash Professional.