Accessing class member from another class in aspx.cs

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C#

ASP.NET

I am a new bee in asp.net. In a asp.net application there is
a class named "DataAccessLayer.cs" use to connect database.
In another page i.e. index.aspx when i am using...

namespace WebApp 
{
    public partial class index : System.Web.UI.Page
    {
        DataAccessLayer objDataAccessLayer = new DataAccessLayer(); 
        
        protected void Page_Load(object sender, EventArgs e)
        {

        }
    }
}

it runs in my localhost success fully. but it generate error
when i am hosting it.

Error say: CS0246: The type or namespace name 'DataAccessLayer' could not be found (are you missing a using directive or an assembly reference?)

What I have tried:

I have make a class library file in another project and in another solution i add the class library and above project together. then add reference. but all are in vain.