Custom Validation

Can someone please explain to me how the validation works in the 4.5 version. If I remove the "Email Required" on the model and let the business layer catch the error by adding the AddRule for email required it will still go through and thrown an error in the DAL. I thought in version 4.0 the business caught the error and put it up in the screen. Example: in version 4.0 I removed "Company Required" on the Model class and let the business layer catch it, it seemed to correctly put the error on the screen for adding a member. Now, if I removed the validation on the model class it goes all the way to the DAL and throws an error there. Any help on why this is and how to let BAL correctly handle and throw errors on the screen.


Thanks
Dennis