Calculated Item dialog window does not show up. Bug?

This is weird. I am trying to  insert a calculated item for a picot table.

The calculated item menu is not greyed out but when I click the dialog box does not show up...

I can add a calculated field (the menu window does show up in this case) but somehow not for the item.

I  have tried using the simplest form of pivot table in a separate sheet and still does not show up.

Any help?