Bueno creo que hace mas de 2 dias hando con este error y ya estoy medio cansado llevo buscando info y la verdad no logro encontrarle la solucion y me preguntaba si alguien de aqui me podria ayudar.Estoy tratando de hacer una conexion a una base de datos MS SQL server 2008, con c# y estoy usando visual studio 2015, tengo agregada a mi proyecto la dll (System.data.dll) pero aun asi me sigue dando el error.mi error es el siguiente:

Unhandled Exception: System.TypeLoadException: Could not load type 'System.Data.SqlClient.SqlConnection' from assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.  at (wrapper managed-to-native) System.MonoType:GetMethodsByName (string,System.Reflection.BindingFlags,bool,System.Type)  at System.MonoType.GetMethods (BindingFlags bindingAttr) [0x00000] in <filename unknown>:0  at Mono.CSharp.MemberCache.AddMethods (BindingFlags bf, System.Type type) [0x00000] in <filename unknown>:0  at Mono.CSharp.MemberCache.AddMethods (System.Type type) [0x00000] in <filename unknown>:0  at Mono.CSharp.MemberCache..ctor (IMemberContainer container) [0x00000] in <filename unknown>:0  at Mono.CSharp.TypeHandle..ctor (System.Type type) [0x00000] in <filename unknown>:0  at Mono.CSharp.TypeHandle.GetTypeHandle (System.Type t) [0x00000] in <filename unknown>:0  at Mono.CSharp.TypeHandle.GetMemberCache (System.Type t) [0x00000] in <filename unknown>:0  at Mono.CSharp.TypeManager.MemberLookup_FindMembers (System.Type t, MemberTypes mt, BindingFlags bf, System.String name, System.Boolean& used_cache) [0x00000] in <filename unknown>:0  at Mono.CSharp.TypeManager.RealMemberLookup (System.Type invocation_type, System.Type qualifier_type, System.Type queried_type, MemberTypes mt, BindingFlags original_bf, System.String name, IList almost_match) [0x00000] in <filename unknown>:0  at Mono.CSharp.TypeManager.MemberLookup (System.Type invocation_type, System.Type qualifier_type, System.Type queried_type, MemberTypes mt, BindingFlags original_bf, System.String name, IList almost_match) [0x00000] in <filename unknown>:0  at Mono.CSharp.Expression.MemberLookup (Mono.CSharp.CompilerContext ctx, System.Type container_type, System.Type qualifier_type, System.Type queried_type, System.String name, MemberTypes mt, BindingFlags bf, Location loc) [0x00000] in <filename unknown>:0  at Mono.CSharp.Expression.MemberLookupFinal (Mono.CSharp.ResolveContext ec, System.Type qualifier_type, System.Type queried_type, System.String name, MemberTypes mt, BindingFlags bf, Location loc) [0x00000] in <filename unknown>:0  at Mono.CSharp.New.DoResolve (Mono.CSharp.ResolveContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.Expression.Resolve (Mono.CSharp.ResolveContext ec, ResolveFlags flags) [0x00000] in <filename unknown>:0  at Mono.CSharp.Expression.Resolve (Mono.CSharp.ResolveContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.Assign.DoResolve (Mono.CSharp.ResolveContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.SimpleAssign.DoResolve (Mono.CSharp.ResolveContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.Expression.Resolve (Mono.CSharp.ResolveContext ec, ResolveFlags flags) [0x00000] in <filename unknown>:0  at Mono.CSharp.Expression.Resolve (Mono.CSharp.ResolveContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.ExpressionStatement.ResolveStatement (Mono.CSharp.BlockContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.StatementExpression.Resolve (Mono.CSharp.BlockContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.Block.Resolve (Mono.CSharp.BlockContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.Block.Resolve (Mono.CSharp.BlockContext ec) [0x00000] in <filename unknown>:0  at Mono.CSharp.ToplevelBlock.Resolve (Mono.CSharp.FlowBranching parent, Mono.CSharp.BlockContext rc, Mono.CSharp.ParametersCompiled ip, IMethodData md) [0x00000] in <filename unknown>:0 [/quote] Mi Codigo C# qe estoy utilizando:
 

using UnityEngine;
using System.Collections;
using System;
using System.Data;
using System.Data.SqlClient;

public class SQLTest : MonoBehaviour {

    public static SqlConnection ObtenerConexcion()
    {
        string conn_str = "Server=home.z3nth10n.net; Database=psdb; User Id= sa; Password=1234";
        SqlConnection conn = new SqlConnection(conn_str);
        conn.Open();
        return conn;
    }
  

    // Use this for initialization
    void Start () {
           
         
}


    // Update is called once per frame
    void Update () {

}


    void OnGUI() {
        GUI.Box(new Rect(20, 20, 250, 250), "CREAR CUENTA");
        GUI.Label(new Rect(40, 100, 50, 25), "Usuario: ");
        GUI.Label(new Rect(40, 135, 50, 25), "Contra: ");
        GUI.Label(new Rect(40, 170, 50, 25), "Correo: ");
        GUI.TextField(new Rect(100, 100, 100, 25), "");
        GUI.TextField(new Rect(100, 135, 100, 25), "");
        GUI.TextField(new Rect(100, 170, 100, 25), "");
        GUI.Button(new Rect(40, 210, 100, 25), "Crear Cuenta");
        if (GUI.Button(new Rect(160, 210, 100, 25), "Cancelar")) {
            Application.Quit();
            Debug.Log("Se Cancelo El Registro");

        }
    }

}

 Espero que me puedan ayudar desde ya muchas gracias a todos los que por lo menos lo intenten

"Server=home.z3nth10n.net; Database=psdb; User Id=sa; Password=1234; Integrated Security=True"

Quita es espacio en User ID= sa también.

[quote author=iRobb date=1440059977" data-ipsquote="" data-cite="iRobb" class="ipsQuote">

"Server=home.z3nth10n.net; Database=psdb; User Id=sa; Password=1234; Integrated Security=True"

system.data de visual estudio y por eso me daba el error, cuando enrealidad las dll qe debo usar son las de monodevelop.Nuevamente Te Agradesco Tu Respuesta