Disable ribbon element if workbook doesnt contain a specific worksheet

Hi all,

I think I'm pretty close to figuring this one out, but I still need an experts opinion/advice:

Following xml is used:

	<button id="rxCalculate"
							label="Hiring Plan Calculate"
							imageMso="RecurrenceEdit"
							size="large"
							onAction="rxbtnCalculate"
							getEnabled ="rxCalculate_getEnabled"/>

Following VBA used:

'Callback for rxCalculate getEnabled
Sub rxCalculate_getEnabled(control As IRibbonControl, ByRef returnedVal)
    
Dim x As Boolean
Dim Worksheet As Worksheet
Dim CurrentWb As Workbook

Set CurrentWb = ActiveSheet.Parent

For Each Worksheet In CurrentWb
    If Worksheet.Name = "Wkly. Sum." Then x = True
Next Worksheet

Select Case x
    
    Case Is = True
        returnedVal = True
    Case Is = False
        returnedVal = False
End Select

End Sub

Even if the code is ok, it wont work since there won't be any worksheet when the UI loads(only the application window). How should i proceed? Basically i want a specific ribbon button to be disabled when the current workbook doesnt contain a worksheet named "Wkly. Sum."

Thanks