The NFSC dough isn't my recipe, but it is one I use every day. The dough should be soft and very easy to roll out....even fresh after you've made it. If it is crumbly, your butter was too cold/hard (solution = it should be soft enough to stick your finger right through it, if not then nuke it for 10-20 seconds first so that it is really soft) OR your flour measurement is not accurate (I weigh my a.p. flour at 150 grams per cup, rather than scooping....which isn't accurate at all) OR you haven't let the mixer work the dough enough (I leave mine on lowest speed with the paddle attachment for 30-90 seconds. The dough is not donw mixing until it pulls away from the sides of the bowl and forms a nice clean ball.)
Try these 3 things and your dough will be better. 
Here's a NFSC help multi-linked thread:
http://forum.cakecentral.com/cake-decorating-ftopict-69731.html
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