/// Gets the key fields and places them in a string


public class GetKeyFields
{
    public GetKeyFields _fields = new GetKeyFields();
}

public string  keyString
{
    get
    {
        if (keyString.Length == 0)
        {
            StringBuilder sb = new StringBuilder();
            // LOOP THROUGH THE Fields AND BUILD THE KEY
            foreach (FieldClass field in this.Fields.**GetKeyFields**())
            {
                sb.Append(field.Name + ", ");
            }
            keyString = sb.ToString().TrimEnd(new char[] { ',', ' ' });
        }
        return keyString;
    }
}

'ProfileClass.FieldCollectionClass' does not contain a definition for 'GetKeyFields' and no extension method 'GetKeyFields' accepting a first argument of type 'ProfileClass.FieldCollectionClass' could be found(are you missing a using directive or an assembly reference?)