.NET Custom Configuration Section

I created a custom configuration section using the System.Configuration.ConfigurationSection class.

I'm have created a class that extends the ConfigurationElementCollectionClass -  to represent a configuration element containing a collection of child elements.

The class works fine when retrieving values from the configuration file, but when I try to remote an object of this type, I get the following exception:

"You must implement a default accessor on
System.Configuration.ConfigurationLockCollection because it inherits
from ICollection."

In my class that extends ConfigurationElementCollection, I have the following accessor

        public ManufacturerConfigurationElement this[int index]
        {
            get
            {
                return (ManufacturerConfigurationElement)BaseGet(index);
            }
            set
            {
                if (BaseGet(index) != null)
                {
                    BaseRemoveAt(index);
                }

                BaseAdd(index, value);
            }
        }

Any ideas why I'm still receiving this exception?

Thanks,