Do you measure or weigh your flour? I've found since I've started weighing the flour my cookies are pretty consistent.
Did you change any ingredients or brand names? Are your eggs the same? I accidently bought large instead of extra large once.
Just trying to play devil's advocate for you.
Hope you get it figured out as I know it can be very frustrating. Good luck.
Now that you said this I noticed that the last time my cookies were also crumbly sort of....I couldn't figure out what I did wrong because I've done this recepie so many times that I know it by heart.
But, as Kimsmom said, maybe the flour weight, the size of eggs etc...I may have used a different brand of butter too.
I only make a half recipe at a time (because my mixer is smaller than the new KAs) I use 1 extra large egg, because that's what I use for everything else, and the flour is 14oz. (28oz. for a full recipe). But you might use less because your eggs are smaller. It's a trial and error type of thing, but once you get your perfect recipe it should work every time. I got my figure by measuring out the number of cups it called for in the recipe, using sifted flour, and weighed it on a scale. The cookies were perfect so I kept this weight.
I always weigh my flour as it keeps it consistent and hey, it is faster! I would suggest that you keep weighing it until you find the one that works agian and use that weight each time. It just is so much easier that way. For me (on my scale), I use 1 lb 12 oz of flour for the NFSC, but that is just what works for me and my scale.
Definitely weigh out your flour. I too had problems with the dough being too dry before I got a scale. I use 31.8 ounces of flour (not good at math, not sure if that is what you use too, TracyLH!). 
kimsmom, TracyLH, and MichelleM77 - can you tell me exactly what scale you use to weigh your flour and where you would get one? I'm thinking of going this route myself. And about how much do they cost?
Mine is battery operated by Salter. It's very compact and will let you weigh on the base alone, or you can add a very large bowl and measure that way. (this is how I weigh my flour) I can't remember how much I paid for it, but I bought it at Bed Bath and Beyond using a 20% off coupon. I remember I thought it was well worth the money. I also use it to weigh my powdered sugar for icing. Hope that helps.
I recently purchased a scale at Ross. I think it cost about $10. It has a little bowl that sits on top and the scale fits inside the bowl for storage. They also had some digital ones, but I didn't see the need. Since weighing food is common for people with specialized diets, you can find food scales almost anywhere, especially in the kitchen gadgets sections of WalMart, Target, etc.
Weighing is a lot quicker than measuring out and it ensures consistency since flour and powder sugar can "settle" or become compacted, creating inconsistencies when measuring out. When you weight a pound of flour, you get a pound of flour - regardless of the volume.
Keep in mind, if you are measuring your ingredients into a bowl or other container, place the empty container on the scale first and make sure the scale reads "0". Then add your ingredients to the container. The weight of your container is called the "tare" weight and you don't want to include that weight in your measurements.
My motivation to purchase the scale was the Antonia74 RI recipe, which states the powdered sugar by weight. Also, I buy powdered sugar in bulk, so I can now measure out 1 lb. or 2lbs. of powdered sugar, which are commonly stated as ingredients (instead of cups) because those are common retail package weights in the U.S.
Hope this helps.
i've come across this issue before and I realized I didn't mix my dough long enough. I use a KA and after all the ingredients are mixed, I let the mixer run until the cookie dough forms into a mass of dough and there's no evidence of extra ingredients (like the flour, sugar etc.).
I haven't personally weighed my ingredients, but I think i'll try it next time. I also have the small salon scale.
HTH 
Hi again! To answer your question, I have been using a battery operated Salter for years and I got it as a gift from my DH, so I don't know where he got it. As he is 'gadget man', he picked up a really slick Terralion Pro 1002 in the clearance bin at Williams-Sonoma and I really liked it when I tried it out. It has a much larger base than the Salter, but honestly, I just reach for my little Salter as it is small and right where I can get to it easily.
I use it to weigh my flour (1 lb. 12 oz.) for the NFSC recipe, but don't weigh the sugar usually as it is handy enough to scoop it out when I am doing the butter, but I like toleshed's idea to do that as well. I also use it to weigh the 2.25 lbs. of powdered sugar in Antonia74's R.I. recipe. Weighing saves me time and gives me the accuracy I want. I really recommend it!
How funny, I have had problems with the NFSC recipe, but the opposite problem! Even after being refridgerated for quite some time it was way too soft and sticky, so I always follow the recipe and then add more flour until I like the consistency. I wonder if it has to do with the high altitude here? Either way, they taste yummy and I get lots of complements!
I would have said not enough butter, right from the get-go. I have always just "eye-balled" my butter, but then I had some problems, and started weighing my butter. No more problems! I still don't weigh anything else. I'm naughty that way.
Also, I find that if I mix my cookies by hand they turn out way better than if I use my mixer. It might have to do with a gentle hand, I really don't know. Good luck!
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