Formatdate Function

Hi All,

I have a column valid To representing 12/31/99-mm/dd/yyyy.

So I used =formatdate([Valid To];"dd/mm/yyyy") to convert  mm/dd/yy as dd/mm/yyyy .

But I got the result as 31/59/9999 i.e., got in correct data for mm .

Kindly let me know ,how to solve this ?

Thanks

Ram