Pivot Table, Blank Field and Grouping

Hi,

I am trying to group by dates (month/quarter) using a dynamic Pivot Table,

I had it up and running until a blank date field was entered.

Any ideas on how i can resolve this?

I have tried filtering the data to not include blank fields but then i get 'cannot group that selection'....frustrating!

Thanks
Bon

Can you attach a sample to look at?