Unique key constraint when saving in entity framework 3.5

I use EF 3.5 and have a db with a category table. I've created a partial class to expand the class created by EF. I have CategoryId as a key in the db and it is set to Identity in the model. This is my partial class:

public partial class Category
{

    public Category(开发者_JS百科string name, bool isChild)
    {
        this.CatName = name;
        this.IsChild = isChild;
    }

    public bool Save()
    {
        try
        {
            using (var context = new PhonebookEntities())
            {
                context.AddToCategories(this);
                context.SaveChanges();
            }
            return true;
        }
        catch (System.Exception)
        {
            return false;
        }
    }
}

But when I try to create a new Category object and save it..:

        var category = new Category("Test", false);
        category.Save();

I get this exception: "Violation of UNIQUE KEY constraint 'IX_Category'. Cannot insert duplicate key in object 'dbo.Category'.\r\nThe statement has been terminated." I should mention that a category has a reference to itself because it can have a parent category through a nullable int which points to the categoryid to the parent category.

What is the contents of IX_Category? If it is not needed, delete it. Is there another category with "Test" as its CatName in your database? Is IX_Category a unique key constraint on the CatName field?