GETPIVOTDATA #REF Problem with Dates

Happy New Year everyone.

I have a pivot table with some simple row fields which are dates. When I enter a '=' and select a cell in the pivot Excel automatically creates the GETPIVOTDATA string. However, when pressing enter the formula returns #REF?

Has anyone had anything similar?

The only problem is that the Pivot Table is referenced correctly and the arguments refer to a visible field. It's as though it doesn't like the date argument? If I remove the field containing the date, and add one that is 'Customer' lets say, the above process works perfectly.

I'm thinking it has something to do with how the Pivot Table is interpreting and displaying the date field.

Will try and alter the pivot cache and get an exmaple workbook up as it currently contains confidentail information.

Cheers,

Jamie