How do i fix the core CRUD options?

Question

Got a issue with the core CRUD options from this C# app. See .zip file.

 

How do i solve the bug? And what the reason why it's not working .... ?

 

Used software and settings

 

1. MS Management Studio

. Run sql script.

 

2. VS 2017

Connection for db. Add in fonfig file.

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

<startup>

<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2" />

</startup>

<connectionStrings>

<add name="connstrng" connectionString="Data Source= Change it to yours ;

Initial Catalog=RContactApp;Integrated Security=True;"/>

</connectionStrings>

</configuration>