sounds like you have to up the base mesh value in your poly to sub-d options. Go to modify> convert> polygons to sub-d> option box and you should see a number like 1000 rasie it up to about 3000.

The script editor is a little box on the bottom right courner. When you get that error coming up open the box and you can scroll over to the right and it should give you the excate number to put into the bash mesh options. Do this if you dont want to up it randomely.