namespace PhotoSift
{
    /// <summary>
    /// Contains all PhotoSift settings. Most attributes control appearance in the PropertyGrid in frmSettings.
    /// </summary>
    [Serializable]
    [DefaultProperty("FileMode")]
    public class AppSettings : GlobalizedObject
    {
        ...
        // Key Folder group
        [Category("Key Folders"), DisplayName("A"), LocalizedDescription("blablabla")]
        [Editor(typeof(FolderNameEditor2), typeof(UITypeEditor))]
        public string KeyFolder_A { get; set; }
        [Category("Key Folders"), DisplayName("B"), LocalizedDescription("blablabla")]
        [Editor(typeof(FolderNameEditor2), typeof(UITypeEditor))]
        public string KeyFolder_B { get; set; }
        [Category("Key Folders"), DisplayName("C"), LocalizedDescription("blablabla")]
        [Editor(typeof(FolderNameEditor2), typeof(UITypeEditor))]
        public string KeyFolder_C { get; set; }
        [Category("Key Folders"), DisplayName("D"), LocalizedDescription("blablabla")]
        [Editor(typeof(FolderNameEditor2), typeof(UITypeEditor))]
        ....
    }
}

.....
PropertyInfo Prop = ( typeof( AppSettings ) ).GetProperty( "KeyFolder_" + KeyName );
Prop.SetValue(Prop.Name, "new value");
.....

ERROR:
System.Reflection.TargetException: 'Object does not match target type.'