Casting Error when using serialization

I asked this question awhile ago, but didn't get a usuable answer. Basically, I can't get my method for duplicating objects to work due to invalid cast exceptions. But I can cast things fine outside of the duplication method.

Here's the duplication method

public static class ObjectDuplicator
{
    public static T Clone<T>(T source)
    {
        if (!typeof(T).IsSerializable)
        {
            throw new ArgumentException("the Type must be serializable.", "source");
        }

        if (Object.ReferenceEquals(source, null)) //dont try to serialize a null object
        {
            return default(T);
        }

        IFormatter formatter = new BinaryFormatter();
        Stream stream = new MemoryStream();
        using (stream)
        {
            formatter.Serialize(stream, source);
            stream.Seek(0, SeekOrigin.Begin);
            return (T)formatter.Deserialize(stream);
        }
    }
}

The problem is this: when I call this method using the code below

public void AddJob(Job job)
{
    if (!Jobs.Contains(job))
    {
        Job newcopy = Utilities.ObjectDuplicator.Clone<Job>(job);

        Jobs.Add(newcopy);
    }
}

it throws this exception:

System.InvalidCastException was unhandled Message=Unable to cast object of type 'KH.CharacterClasses.Freelancer' to type 'KH.CharacterClasses.Job'

Now, the type of job I'm adding is an inherited class from Job, (Freelancer) and the code for those two classes is below

[Serializable]
public class Job : Ability
{
    protected JobCommand basecommand1;
    protected JobCommand basecommand2;
    protected JobCommand basecommand3;
    protected JobCommand basecommand4;
    protected JobCommand command1;
    protected JobCommand command2;
    protected JobCommand command3;
    protected JobCommand command4;
    bool mastered;
    protected FFJob job;
    protected string name;
    int level;

    public FFJob SetJob
    {
        get
        {
            return job;
        }
    }

    public bool Mastered
    {
        get
        {
            return mastered;
        }
    }

    public JobCommand Command1
    {
        get
        {
            return command1;
        }
        set
        {
            command1 = value;
        }
    }

    public JobCommand DefaultCommand1
    {
        get
        {
            return basecommand1;
        }
    }

    public JobCommand Command2
    {
        get
        {
            return command2;
        }
        set
        {
            command2 = value;
        }
    }

    public JobCommand DefaultCommand2
    {
        get
        {
            return basecommand2;
        }
    }

    public JobCommand Command3
    {
        get
        {
            return command3;
        }
        set
        {
            command3 = value;
        }
    }

    public JobCommand DefaultCommand3
    {
        get
        {
            return basecommand3;
        }
    }

    public JobCommand Command4
    {
        get
        {
            return command4;
        }
        set
        {
            command4 = value;
        }
    }

    public JobCommand DefaultCommand4
    {
        get
        {
            return basecommand4;
        }
    }

    public Job(string name, string description, int jobID)
        : base(name, description, jobID, -1, -1, null, null, -1, -1)
    {
    }

    public static bool operator ==(Job job1, Job job2)
    {
        if (System.Object.ReferenceEquals(job1, job2))
            return true;
        if (((object)job1 == null) || ((object)job2 == null))
            return false;
        return (job1.Name == job2.Name && job1.UID == job2.UID);
    }

    public static bool operator !=(Job job1, Job job2)
    {
        return !(job1 == job2);
    }


    // public abstract void CharacterModifier(BaseCharacter character);

    // public abstract void CharacterDemodifier(BaseCharacter character);
}

[Serializable]
public class Freelancer : Job
{
    public Freelancer()
        : base("Freelancer", "A character not specializing in any class. Can combine the power of all mastered Jobs.", Globals.JobID.ID)
    {
        basecommand1 = JobCommand.Attack;
        basecommand2 = JobCommand.Free;
        basecommand3 = JobCommand.Free;
        basecommand4 = JobCommand.Items;
        command1 = basecommand1;
        command2 = basecommand2;
        command3 = basecommand3;
        command4 = basecommand4;
        job = FFJob.Freelancer;
    }
}

I really don't know what the issue is. As I said, casting works fine outside of this method, and I know this code has worked before. Any ideas?

Thanks