The underlying provider failed on Open. c# code example
Example 1: System.Data.Entity.Core.EntityException: The underlying provider failed on Open
<add name="ConnectionStringName"
providerName="System.Data.SqlClient"
connectionString="Data Source=ServerName\InstanceName;Initial Catalog=DatabaseName; Integrated Security=True;MultipleActiveResultSets=True" />
Example 2: System.Data.Entity.Core.EntityException: The underlying provider failed on Open
<add name="ConnectionStringName"
providerName="System.Data.SqlClient"
connectionString="Data Source=ServerName;Initial Catalog=DatabaseName;Integrated Security=False; User Id=userid;Password=password;MultipleActiveResultSets=True" />