The mdf data base file in your application is not compatible with the 2012 sql server express instance that you have. I would say that it was probably created with a 2008 edition, but that is just a guess, I have not looked at the exercise.
In order to use the mdf file you attach it to your local instance in the connection string. Your local instance must be able to open it.
Last edited by mmorgan30; March 3rd, 2015 at 11:52 PM..