Здравствуйте.

Реквест здесь

Неправильно показывает "Cannot apply indexing to expression of type FluoroRegistryConfiguration". Все там можно.
В одной сборке:

using System;
using System.ComponentModel;
using System.Configuration;
using ConfigurationSection = MedSoft.Plugins.Configuration.ConfigurationSection;

namespace MedSoft.Fluoro.Documents
{
    internal class FluoroRegistryConfiguration : ConfigurationSection
    {
        [ConfigurationProperty("ServiceUrl")]
        [Category("Связь")]
        [DisplayName("Адрес сервера")]
        [Description("Адрес веб-службы на сервере, которая предоставляет данные")]
        public string ServiceUrl
        {
            get { return (string) this["ServiceUrl"]; }
            set { this["ServiceUrl"] = value; }
        }
    }
}

В другой сборке:

using System;
using System.ComponentModel;
using System.Configuration;

namespace MedSoft.Plugins.Configuration
{
    public abstract class ConfigurationSection : System.Configuration.ConfigurationSection
    {
        [Browsable(false)]
        public new ElementInformation ElementInformation
        {
            get { return base.ElementInformation; }
        }

        [Browsable(false)]
        public new SectionInformation SectionInformation
        {
            get { return base.SectionInformation; }
        }

        [Browsable(false)]
        public new ConfigurationLockCollection LockAllAttributesExcept
        {
            get { return base.LockAllAttributesExcept; }
        }

        [Browsable(false)]
        public new ConfigurationLockCollection LockAllElementsExcept
        {
            get { return base.LockAllElementsExcept; }
        }

        [Browsable(false)]
        public new ConfigurationLockCollection LockAttributes
        {
            get { return base.LockAttributes; }
        }

        [Browsable(false)]
        public new ConfigurationLockCollection LockElements
        {
            get { return base.LockElements; }
        }

        [Browsable(false)]
        public new bool LockItem
        {
            get { return base.LockItem; }
            set { base.LockItem = value; }
        }
    }
}