Call VSTO code from VBA

Hi everybody,
I'm trying to call a method exposed VSTO method from VBA. I followed the instructions in http://msdn.microsoft.com/en-us/library/bb608614.aspx.
I successfully build the VSTO project and I can see "ExcelImportData" in the Windows registry. But when I run VBA code:
Sub CallVSTOMethod()
Dim addIn As COMAddIn
Dim automationObject As Object
Set addIn = Application.COMAddIns("ExcelImportData")
Set automationObject = addIn.Object
automationObject.ImportData
End Sub

after
Set addIn = Application.COMAddIns("ExcelImportData")
I see the value of addIn is "ExcelImportData".
addIn.Object returns Nothing.
so I can not run through automationObject.ImportData

I'm developing using VSTO and  not very familiar with VBA, so I appreicate if anybody can help me with this. Thank you very much!!