I get a compile time error with the following relevant code snippet at the line that calls NotifyObservers in the if construct.

public class ExternalSystem<TEmployee, TEventArgs> : ISubject<TEventArgs>
    where TEmployee : Employee
    where TEventArgs : EmployeeEventArgs
{
    protected List<IObserver<TEventArgs>> _observers = null;
    protected List<TEmployee> _employees = null;

    public virtual void AddNewEmployee(TEmployee employee)
    {
        if (_employees.Contains(employee) == false)
        {
            _employees.Add(employee);

            string message = FormatMessage("New {0} hired.", employee);

            if (employee is Executive)
                NotifyObservers(new ExecutiveEventArgs { e = employee, msg = message });
            else if (employee is BuildingSecurity)
                NotifyObservers(new BuildingSecurityEventArgs { e = employee, msg = message });
        }
    }

    public void NotifyObservers(TEventArgs args)
    {
        foreach (IObserver<TEventArgs> observer in _observers)
            observer.EmployeeEventHandler(this, args);
    }
}

The error I receive is:

The best overloaded method match for 'ExternalSystem.NotifyObservers(TEventArgs)' has some invalid arguments. Cannot convert from 'ExecutiveEventArgs' to 'TEventArgs'.

I am compiling this in C# 3.0 using Visual Studio 2008 Express Edition.