Email sending error while changing API compatibility level

Hi All,

This is been a really hard work for me to resolve following error.

I am trying to have a simple mailing functionality for sending users mails via g-mail profile.
The setup works fine when API compatibility level is set to “.net2.0 Subnet” and i am working on unity.
But when i export my project and then try from standalone project on windows , it creates SQL Exception.

Workaround that i found out to make it work is change the API compatibility level to “.net2.0” , but when i change the API compatibility level it creates following error -

Assets/External Scripts/emailWithAttachment.cs(91,49): error CS0433: The imported type `System.Net.Mail.MailMessage' is defined multiple times

Assets/External Scripts/emailWithAttachment.cs(98,49): error CS0433: The imported type `System.Net.Mail.SmtpClient' is defined multiple times

I am using following imports ( C# script) -

using UnityEngine;
using System;
using System.Net;
using System.Net.Mail;  
using System.Collections;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;

Unity version - 4.5.2f1

Please update the correct methodology to follow here.

You have probably some DLL in your plugins folder that already defines System.Net.Mail.MailMessage and System.Net.Mail.SmtpClient