I have the orbital sharpener, and it does work to sharpen a dull blade, but it is hard to remove a nick. what are you using for a mat? And what is your technique for cutting?
IE, how many layers of fabric are you cutting at a time, what type of mat, ruler, cutter?
I only ask this because I had a customer who was placing the fabric on TOP of the ruler, rather than under it, so i think it is best to start with the basics and work from there. Technique *may* have something to do with the problem.