AmbiguousMatchException occuring on previously working tests

I'm getting the following error on several tests that have passed up until this point. I can't point to any changes that may have caused this problem.

The error:
Test method TimeEntryTest.ApplicationFormTest.printToolStripButton_ClickTest threw exception: System.Reflection.AmbiguousMatchException: Ambiguous match found...

The Stack:
at System.DefaultBinder.BindToMethod(BindingFlags bindingAttr, MethodBase[] canidates, Object[]& args, ParameterModifier[] modifiers, CultureInfo cultureInfo, String[] names, Object& state)
at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
at TypeMock.MockManager.MockObject(Type type, Constructor mockConstructors, Object[] args)
at TimeEntryTest.ApplicationFormTest.ExecutePrintTest(String itemOrButton) in C:Documents and SettingscedplghMy DocumentsVisual Studio 2005ProjectsCorporateTimeEntryTimeEntry.rootTimeEntryTimeEntryTestApplicationFormTest.cs:line 1016
at TimeEntryTest.ApplicationFormTest.printToolStripButton_ClickTest() in C:Documents and SettingscedplghMy DocumentsVisual Studio 2005ProjectsCorporateTimeEntryTimeEntry.rootTimeEntryTimeEntryTestApplicationFormTest.cs:line 1003
The Code:

[[TestMethod]
        public void printToolStripMenuItem_ClickTest()
        {
            ExecutePrintTest("item");
        }

        public void ExecutePrintTest(string itemOrButton)
        {
            MockManager.ClearAll();
            MockObject displayControllerMock = MockManager.MockObject(typeof(DisplayController), Constructor.Mocked);
            MockObject timesheetFormMock = MockManager.MockObject(typeof(TimesheetForm), Constructor.Mocked);
            MockObject applicationFormMock = MockManager.MockObject(typeof(ApplicationForm), Constructor.Mocked);

            ApplicationForm target = applicationFormMock.Object as ApplicationForm;
            DisplayController displayController = displayControllerMock.Object as DisplayController;
            TimesheetForm timesheetForm = timesheetFormMock.Object as TimesheetForm;


            applicationFormMock.ExpectGet("DisplayController", displayController);
            applicationFormMock.ExpectGet("ActiveMdiChild", timesheetForm);
            displayControllerMock.ExpectCall("PrintTimesheet").Args(timesheetForm);

            Corporate_TimeEntry_Client_ApplicationFormAccessor accessor = new Corporate_TimeEntry_Client_ApplicationFormAccessor(target);

            if (itemOrButton == "button")
            {
                accessor.printToolStripButton_Click(timesheetForm, null);
                return;
            }
            if (itemOrButton == "item")
                accessor.printToolStripMenuItem_Click(timesheetForm, null);

        }

The error occures at this line:

 MockObject timesheetFormMock = MockManager.MockObject(typeof(TimesheetForm), Constructor.Mocked);

Any ideas?