字符串输入的格式不正确，带有负浮点数 - C＃

Question

我试图在C＃中反序列化一个基本的xml文件。这是反序列化代码：

using (var reader = new StreamReader("Plugins/LSPDFR/LSPSAddonCallouts.xml"))
        {
            XmlSerializer deserializer = new XmlSerializer(typeof(List<Custom.CustomMission>),
              new XmlRootAttribute("CustomMissions"));
            customMissions.AddRange((List<Custom.CustomMission>)deserializer.Deserialize(reader));
        }

但运行代码时出现此错误：

Errore nel documento XML (9, 4).   in System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
[11/04/2017 10:56:51.346] in System.Xml.Serialization.XmlSerializer.Deserialize(TextReader textReader)
        [11/04/2017 10:56:51.347] System.FormatException: Formato della stringa di input non corretto.
    [11/04/2017 10:56:51.347] in System.Number.ParseSingle(String value, NumberStyles options, NumberFormatInfo numfmt)
    [11/04/2017 10:56:51.347] in System.Xml.XmlConvert.ToSingle(String s)
    [11/04/2017 10:56:51.348] in Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderList1.Read2_CustomMission(Boolean isNullable, Boolean checkType)
    [11/04/2017 10:56:51.348] in Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderList1.Read3_CustomMissions()

导致我的xml文件出现问题的行是这一行：

<startposprotaY>-726.2017f</startposprotaY>

在此行之前还有其他浮点数被反序列化而没有任何问题，但是这个不会。与其他浮点数的唯一区别是，这是xml文件的唯一负浮点数，其他浮点数是正数。