Can you help me troubleshoot my crumbly cookies?

I made sugar cookies using this recipe: a href="http://allrecipes.com//Recipe/easy-sugar-cookies/Detail.aspx" rel="nofollow"http://allrecipes.com//Recipe/easy-sugar…/a and the dough turned out really crumbly. Due to my son's egg allergy I used flaxseed as a replacement. Could that be the problem?