I am using .ToString("#,##0.00") to format a number.
I'm sure I have used this before but today it doesn't work.

I want to format a System.Double value from the datatable like this 12345.6789 to 12,345.68

Code:
myString = dt.Rows(i)("column_name").ToString("#,##0.00")
gives a System.InvalidCastException:

Conversion from string "#,##0.00" to type 'Integer' is not valid.

Any ideas?