Suggestion
Use a program that doesn't leave a watermark if you're only using a trial. I'm assuming you are using a different program, and then exporting into flash to make it .swf and for adding the preloader. If that is the case, I would recommend that you try to edit the movie together in flash. It may take the slightest bit more effort (Not much though), but at the very least it would get rid of the watermark.