I do not know if this will help, but it might be worth a try.
Please consider the following thread.
What I am suggesting that you might try, if your original artwork is in a file that can be loaded into Microsoft Paint, is to load a copy of your original artwork into Microsoft Paint, then save with a different name so as not to alter the original, then, in Paint, use Image Stretch/Skew… and in the Stretch section use 400% for Horizontal and 400% for Vertical, leaving the 0 values in the Skew section unaltered, then click OK, then Save.
Then try importing that new image file into FontCreator.
At first glance, what I suggest may seem pointless as the artwork file is just bigger without being of any greater resolution: however, sometimes the bitmap to vector conversion process of FontCreator does seem then to produce a better result on such an enlarged image.
So, if you try the above idea it may not improve your results.
If you do try it, please let us know your results.
I hope that this helps.
William Overington
11 June 2009