This part only works in the A1278 MacBook. It will not work in a A1278 MacBook Pro even though the model number is the same.
Make sure you have identified your Mac correctly. You can ID Your Mac here. Do these simple steps and save yourself a lot of frustration!
Identify your Mac
2 or 2.4 GHz Unibody (Model No. A1278) 13" MacBooks
Model #: A1280