cant add script component, because the script class cannot be found

my unity script is crashing when trying to run. im trying to access .dll files since i use c++ code and the script is suppossed to call these. the code does not give any errors but when running i get this message "cant add script component, because the script class cannot be found" this is my code, can anyone see why it refuses to run

 using UnityEngine;
 using System.Collections;
 using System.Runtime.InteropServices;
 using System.IO;
 
 public class UseDll : MonoBehaviour
 {
     
     // Straight From the c++ Dll (unmanaged)
     [DllImport("SpheroDefender15338", EntryPoint = "TestDivide")]
     public static extern float StraightFromDllTestDivide(float a, float b);
     
     // Use this for initialization
     void Start()
     {
         
         /* */
         // Call  the C# DLL SharpMultiply function
         float multiplyResult = TestCSharpLibrary.TestCSharpLibrary.SharpMultiply(3, 5);
         
         // Call the C# DLL TestDivide function which relies on the C++ DLL for this functionality
         float divideResult = TestCSharpLibrary.TestCSharpLibrary.TestDivide(15, 3);
         
         float straightFromDllDivideResult = StraightFromDllTestDivide(20, 5);
         
         // Print it out to the console
         Debug.Log(multiplyResult);
         Debug.Log(divideResult);
         Debug.Log(straightFromDllDivideResult);
         
         // Write the result into a file, so we can even see it working in a build
         using (StreamWriter writer = new StreamWriter("debug.txt", true))
         {
             writer.WriteLine(multiplyResult);
             writer.WriteLine(divideResult);
             writer.WriteLine(straightFromDllDivideResult);
         }
         /* */
         
     }
     
     // Update is called once per frame
     void Update()
     {
         
     }
 }