There are 3 possible reasons when your crust falls apart. 1. The pecans were not chopped finely enough. Make sure they are really fine or they wont hold together. If you press the chopped pecans together and they just fall apart, chop them some more. 2. You didn't press it firmly enough into the pie plate. Make sure that you quite firmly pressing the mixture into the pie tin or plate in an even layer. 3. You didn't bake it long enough. The crust should be a golden brown and a little more brown around the top edges.