How to regenerate private accessor when the member specified could not be found

I am getting the error message saying:

The member specified(SetModelFactory) could not be found. You might need to regenerate your private accessor, or the member may be private and defined on a base class. If the latter is true, you need to pass the type that defines the member into PrivateObject's constructor.

I do try the suggestion at here, but do not work.

public void SetModelFactoryTest()
    {
        AvailabilityBL target = new AvailabilityBL();
        AvailabilityDS ds = new AvailabilityDS();
        ds.EnforceConstraints = false; 
        TestBusinessLogic.BusinessLogic_AvailabilityBLAccessor accessor = new TestBusinessLogic.BusinessLogic_AvailabilityBLAccessor(target);

        // SETUP STANDARD TEST DATA
        this.SetupTestData(ds, null);
        int newModelID = 89;

        // ADD A DUMMY MODEL ROW
        this.SetupTestModel(newModelID, ds);
        accessor.mAvailabilityDS = ds;

        int siteID = 22;
        int platformID = 33;
        string factoryName = "MY COOL FACTORY";
        DateTime validUntil = new DateTime(2015, 9, 27);

        accessor.SetModelFactory(siteID, platformID, factoryName, validUntil);

        Assert.AreEqual(siteID, accessor.mAvailabilityDS.Model[0].SiteID, "SetModelFactory did not set the SiteID.");
        Assert.AreEqual(platformID, accessor.mAvailabilityDS.Model[0].PlatformID, "SetModelFactory did not set the PlatformID.");
        Assert.AreEqual(factoryName, accessor.mAvailabilityDS.Model[0].FactoryName, "SetModelFactory did not set the FactoryName.");
        Assert.AreEqual(validUntil, accessor.mAvailabilityDS.Model[0].ValidUntil, "SetModelFactory did not set the ValidUntil.");
    }

VSCodeGenAccessors.cs

internal void SetModelFactory(int siteID, int platformID, string factoryName, global::System.DateTime validUntil) {
    object[] args = new object[] {
            siteID,
            platformID,
            factoryName,
            validUntil};
    m_privateObject.Invoke("SetModelFactory", new System.Type[] {
                typeof(int),
                typeof(int),
                typeof(string),
                typeof(global::System.DateTime)}, args);
}