Method get_XXX from assembly YYYY does not have an implementation

I am getting the above error message.

I have an abstract class which defines a method like so:

public abstract IContainer NewDal { get; }

-
Then I have a class which is implementing the abstract class like

public class PRegister : AbClass
{
public override IContainer NewDal
{
   get
   {
        return new Dal();
   }
}
}


-
Seems ok to me, but I am getting the error as mentioned above when i run my website

Method get_NewDal from assembly YYYY does not have an implementation


Anyone have any idea why this would be the case?
If it were not implemented, it would not compile in the first place, correct?