An object instance is required for the nonstatic method

Jeg har følgende klasse:

using System;
using System.Data;
using DALComponents;

namespace jmhegn.ProductCatalog
{
    /// <summary>
    /// Summary description for Products.
    /// </summary>
    public class ProductCatalog
    {

        public static DataTable GetCategories(int parentCategory)
        {
            IDbProviderFactory factory = new cSqlProviderFactory();
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=jm.mdb";
            IDbConnection connection = factory.CreateConnection(connectionString);
            factory = new cOleDbProviderFactory();
            connection = factory.CreateConnection(connectionString);
            connection.Open();
            IDbCommand command;
            string commandString = "SELECT * FROM varegrupper WHERE hovedgruppe=" + parentCategory.ToString();
            command = factory.CreateCommand(commandString, connection);
            IDbDataAdapter da = factory.CreateDataAdapter(command);
            DataSet ds = new DataSet();
            da.Fill(ds);
            DataTable dt = ds.Tables[0];
            return dt;
        }

    }
}


Og en codebehind med følgende kode:

foreach(DataRow dr in jmhegn.productCatalog.Products.GetCategories(0))
                {
               
                }

Men jeg får fejlen:

C:\Inetpub\wwwroot\jm\controls\leftMenu.ascx.cs(23): An object reference is required for the nonstatic field, method, or property 'jmhegn.productCatalog.Products.GetCategories(int)'

Er der nogen der kan fortælle mig hvorfor???