Unexpected Unexpected Call Exception

I'm trying to tests the creation of a SPWorkflowAssociation object, but for some unknown reason TypeMock (using AAA) keeps telling me that there was an unexpected call to the method I was expecting a call to.

Exception Message:

Test method BizColostateFeatureReceiverToolsTest.ListToolKitTest.AssociateWorkflowWithlistTestNewWorkflow threw exception: TypeMock.VerifyException:
TypeMock Verification: Unexpected Call to Microsoft.SharePoint.SPList.AddWorkflowAssociation().

The Calling code looks like this:

association = AssociateWorkflow(workflowTemplate, associatedWorkflowName, taskList, historyList, allowManual, autoStartCreate, autoStartChange, associationData);

association = targetList.AddWorkflowAssociation(association); // This is the line the TypeMock exception is being thrown on.

And the relevant test code looks like this:

// set up fake workflow template
Isolate.WhenCalled(() => SPWorkflowAssociation.CreateListAssociation(fakeWorkflowTemplate, associatedWorkflowName,fakeTaskList, fakeHistoryList)).WillReturn(fakeWorkflowAssociation);

Isolate.WhenCalled(() => fakeTargetList.AddWorkflowAssociation(fakeWorkflowAssociation)).WillReturn(fakeWorkflowAssociation);

Any thoughts would be appreciated!