How to get a method of a class using object?

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C#

I'm doing a asp.net project by n-tier architecture. But when i use a packare suppose Business Logic layer package in UI layer and create a instance of a class of that packege and than try to call a method using that object than i coouldn't find any method of that class. I'm giving a example-

using ENSII.BAL;

protected void ButtonAddCat_Click(object sender, EventArgs e)
{
        string category = TextBoxCat.Text;

        CatagoryHierarchy cat = new CatagoryHierarchy();

        cat.{can't get required method of BAL.CatagoryHierarchy to use}
}