Registering a type with multiple constructors and string dependency in Simple Injector

There are two things about your class that prevents Simple Injector from being able to auto-wire your DAL class:

1. Your class has two constructors and
2. If you remove the default constructor, primitive types such as strings can't be injected.

Nemesv is almost right in his comment. You can fallback to using a delegate registration like this:

container.Register<IDAL>(() => new DAL("db"));

This article describes why your application components should have only one constructor.