how to include .net framework assembly dlls into load runner .net script

I have written using System.Data.SqlClient; at  the beginning of script .

but on compiling I get this error" The type or namespace name 'Data' does not exist in the namespace 'System' (are you missing an assembly reference?)".

How to resolve this.

Please Help..

I m stuck for the past 2 days. I want to do POT