Converting a string to date after pivoting data

Hi There,

I have a data set where dates are listed on the top row, formatted as mmm-yy, with values below.

E.g.   

When connecting to my data, I have pivoted the data so that the columns are now Date | Product | Pivot Field Values

However the date has converted to string...

Changing the data type to 'Date' results in Null values.

Creating a calculated field using DATEPARSE("mmm-yy",[Date]) also results in Null values.

Can anyone help?

Thanks,

Catherine