Using dll's from C#?

Hello

I am trying to use a dll I made in C# .net 2.0 without any luck. From what I have read, the dll should be placed in the asset folder and can then be used as any other scripts.

My Dll:

 using UnityEngine;
 using System;
 using System.Collections.Generic;
 using System.Text;
 
 public class SerialGPS_DLL2 : MonoBehaviour
 {
     public void SerialGPSInit(string comPort, int baudRate)
     {
         //Some code
     }
 
     public void SerialGPSClose()
     {
         //Some code
     }
 
     public void SerialGPSUpdate(ref double latitude, ref double longitude, ref string status)
     {
         //Some Code
     }
 }

How I use it: Adding dll as referance in Visual Studio(just to get intellisense).

 using UnityEngine;
 using System.Collections;
 using System.Runtime.InteropServices;

 public class SerialGPS : MonoBehaviour 
 {
     private SerialGPS_DLL2 m_cSerialGPS_DLL;
     
     void Start () 
     {
         m_cSerialGPS_DLL.SerialGPSInit("COM3", 4800);
     }
 
     void Update()
     {
 
     }
 }

The error i get:

 Internal compiler error. See the console log for more information. output was:
 Unhandled Exception: Mono.CSharp.InternalErrorException: Assets/SerialGPS.cs(5,14): SerialGPS ---> Mono.CSharp.InternalErrorException: Assets/SerialGPS.cs(12,28): SerialGPS.m_cSerialGPS_DLL ---> System.TypeLoadException: Could not load type 'SerialGPS_DLL2' from assembly 'SerialGPS_DLL2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
   at (wrapper managed-to-native) System.Reflection.Assembly:InternalGetType (System.Reflection.Module,string,bool,bool)
   at System.Reflection.Assembly.GetType (System.String name, Boolean throwOnError, Boolean ignoreCase) [0x00000] in <filename unknown>:0 
   at System.Reflection.Assembly.GetType (System.String name) [0x00000] in <filename unknown>:0 
   at Mono.CSharp.SimpleName.Error_TypeOrNamespaceNotFound (IMemberContext ec) [0x00000] in <filename unknown>:0 
   at Mono.CSharp.SimpleName.ResolveAsTypeStep (IMemberContext ec, Boolean silent) [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Expression.ResolveAsBaseTerminal (IMemberContext ec, Boolean silent) [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Expression.ResolveAsTypeTerminal (IMemberContext ec, Boolean silent) [0x00000] in <filename unknown>:0 
   at Mono.CSharp.MemberBase.ResolveMemberType () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.MemberBase.Define () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Field.Define () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.TypeContainer+MemberCoreArrayList.DefineContainerMembers () [0x00000] in <filename unknown>:0 
   --- End of inner exception stack trace ---
   at Mono.CSharp.TypeContainer+MemberCoreArrayList.DefineContainerMembers () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.TypeContainer.DefineContainerMembers (Mono.CSharp.MemberCoreArrayList mcal) [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Class.DefineContainerMembers (Mono.CSharp.MemberCoreArrayList list) [0x00000] in <filename unknown>:0 
   at Mono.CSharp.TypeContainer.DoDefineMembers () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Class.DoDefineMembers () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.TypeContainer.Define () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.ClassOrStruct.Define () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Class.Define () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.RootContext.PopulateTypes () [0x00000] in <filename unknown>:0 
   --- End of inner exception stack trace ---
   at Mono.CSharp.RootContext.PopulateTypes () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Driver.Compile () [0x00000] in <filename unknown>:0 
   at Mono.CSharp.Driver.Main (System.String[] args) [0x00000] in <filename unknown>:0 

My only theory at the moment is that I am building my dll in a way that is not supported.