If your crust is coming off it could mean that the cake is baking at too high a temperature, or that it's overbaking, even by a small amount. The crust is made from sugars rising to the top, and so if the cake is overbaked then these sugars can detatch and/or become overly brown.

You might try preheating the oven 50 degrees higher than your recipe specifies, then lower the thermostat to the recipe-specified temp immediately after you put the cake in. This ensures that the oven temperature will be more even because the simple act of opening the door after pre-heating and placing the cake in can really drop the temperature by a significant amount.

I hope this will help.