Error 1004 unable to set the visible property of the pivotitem class

The error you mentioned means it can't find the value of your dropdown selection among the pivotitem choices. Try putting

Option Compare Text

at the top of the module to make it non-case sensitive. This will ensure that whether you choose "a" or "A" that the correct value will be chosen. Without that option an error such as you're describing could happen.

I've posted a new sample workbook, tested to ensure it will work no matter what the selection. Give it a whirl (go to Sheet 1)