notesbitmapをC#で画像として保存

前提・実現したいこと

現在、指定したNotesDBの文書から画像を取得してローカルの保存するツールを作成しています。
文書ごとにDXLを取得してXMLNodeに対して処理を行っています。
画像がGIF,JPG,PNGの時は問題なく動作するのですがnotesbitmapの場合はエラーが出ています。

発生している問題・エラーメッセージ

例外：使用されたパラメータが有効ではありません。


場所 System.Drawing.Image.FromStream(Stream stream, Boolean useEmbeddedColorManagement, Boolean validateImageData)
場所 System.Drawing.Image.FromStream(Stream stream)
場所 NotesConvert.CreateImage.makeImage(Byte[] Bytes)
場所 NotesConvert.CreateImage.getImage(string base64str, string path)
場所 C:\[ファイルパス]\NotesConvert\CreateImage.cs:行 446

該当のソースコード

C#
1      private void getImage(string base64str, string path){
2            byte[] bytes = Convert.FromBase64String(base64str);
3            Image img = makeImage(bytes);
4            img.Save(path);
5      }
6
7      private Image makeImage(byte[] Bytes){
8            MemoryStream ms = new MemoryStream(Bytes);
9            Image img = Image.FromStream(ms);
10            return img;
11      }

試したこと

自分で調べてみたところ以下のページが引っ掛かりました。
https://www.agecom.com.au/support/agecomkb.nsf/0/58cbf10f0ab723c9ca25803e006c7de8
$FILEに画像のデータがあるとのことでしたので該当のnotesbitmapの時はfiledataの値を渡すように変更したのですが、変わらず同じエラーが出ています。

<attachmentref name="test.xls" displayname="test.xls"> <picture height="48px" width="239px"> <notesbitmap>xP8gAAEAAQAAAAgAAAAAAAAAAAAAAAAAU1RHMDMwMzWVACYAAAAAAAAAAAAAAAAAAAAAAAAA7wAwAAAAAAAAAAAAAAAAAA==</notesbitmap> </picture> </attachmentref> <item name="$FILE" summary="true" sign="true" seal="true"> <object> <file hosttype="cdstorage" compression="none" flags="storedindoc" encoding="none" name="STG03035" size="3078"> <created> <datetime /> </created> <modified> <datetime /> </modified> <filedata> AQACDAEAmQAcAAAAAAAAAAAAAAAAAAAAAAAAAAAAAQAAAJUAJgAAAAAAAAAAAAAAAAAAAAAAAADvADAACAABAAgAAgAFABMAlgAQBgAAAAAAAAAAAAAoAP4FQA0AxgBAAgHCA0ANAMcAQA0AxgABA0ACAAIDAUANAMYAQA0AxgABA0ACAMIDAQFADQDFAEAMAMcAQAICyAAEAwIDAUANAMQAQAwAxwBAAgPFAsMABQMAAgMBQA0AwwBADADHAAIDBMwAAgMEyAABA8IAAwIDAUANAMIAQAwAxwAHBAMABAMEA8MABgMEAwAEA8gAAQPDAAMCAwFADQABAEAMAMcAEAMEAAMEAwQDAAMEAwQAAwTIAgEDxwFADQBADADHABEEAwAEAAQDBAMEAwQDAAQDAsQAAQLEAAECwwACAgFADQBADADHAAIDBMIACAQABAMEAwQDwgADAwQCxAABAsQAAQLDAAICAUANAEAMAMcAAgQDwwAGBAAEAwQDwwACBAPLAsMAAgIBQA0AQAwAxwACAwTCAA0EAwQABAMEAwQAAwQCxAABAsQAAQLDAAICAUANAEAMAMcAEQQDAAQDBAMEAAQDBAMABAMCxAABAsQAAQLDAAICAUANAEAMAMcAEAMEAAMEAwQDBAAEAwQAAwTLAsMAAgIBQA0AQAwAxwANBAMABAMEAwQDBAAEA8IEAgMCxAABAsQAAQLDAAICAUANAEAMAMcAAgMExwAEAwQDBMIDAgQCxAABAsQAAQLDAAICAUANAEAMAMcAAgQDzAACBAPLAsMAAgIBQA0AQAwAxwBAAgIBAsQAAQLIAAICAUANAEAMAMcAQAIDAQLHAMMCwwACAgFADQBADQDGAAEDwwDHAgEAwwLCAMMCwwACAgFADQBADQDGAAEDwwABAsQAAQLCAMMCwgDDAsMAAgIBQA0AQA0AxgABA8MAAQLEAAECwgDIAsMAAgIBQA0AQA0AxgABA8MAxwIBAMMCwgDDAsMAAgIBQA0AQA0AxgABA8MAAQLEAAECwgDDAsIAwwLDAAICAUANAEANAMYAAQPDAAECxAABAsIAwwLCAMMCwwACAgFADQBADQDGAAEDwwBAAgQBAsIAAgIBQA0AQA0AxgABA0ACAMYAAgIBQA0AQA0AxgABA0ACAMYAAgIBQA0AQA0AxgABA0ACBMcCAQFADQBADQDGAEADBQEBQA0AQB0AxwBAHQDHAEAdAMcAQB0AxwBABADEAAEBwwABAcIAAwEAAcIAAQHLAAEBxQDNAQEAxQHDAMUBAgABQAgAxwABAcIAywHGAAEBwwABAcUAxgEBAMUBwgABAUADAMQAQAQAwwABAcUABwEAAQABAAHEAMYBwgDFAUACBsMAAQHDAAEBwwABAcIAAQFACADFAAEBwwABAcQAAQHEAAEBQAIHAQHCAAMBAAHFAAEBwwABAUADAMMAxAABAcQAAQHEAMgBwgDFAcUAAQHDAM0BxgACAQDCAcIAAQHEAMkBQAIIwwABAcoAwwHEAMMBxADDAUACCQEAxAHEAMMBwwDEAcUAAQHEAAEBxAABAcQAAQHGAAEBwwABAcUAxgHCAAMBAAHFAAEBzgABAcsAxAABAcQAAQFAAgrDAAEBQAILAQHGAAEBwgAFAQABAAHCAAEBxABABAzGAAEBwwABAcIAAQHDAAEBwgABAcMAAwEAAcMAAQHDAAEBwwADAQABxAABAcIAAQHDAAMBAAHEAAEBxAABAcQAywHDAMQBwwDEAcIAAQHCAAMBAAHDAAEBxgABAc4AAQHLAMQAAQHDAAMBAAFAAg3CAAEBwwABAcUAywHEAMIBxQDCAcUAAQHDAAEBwwBAAg4BAUACCwQAAQABxQDCAcUAwgHEAAMBAAHFAMIBxAADAQABxQDCAcQAAQHDAAEBxQABAcQAAQHEAAEBxgABAcMAAQHFAAEBwgAEAQABAMYBxAABAc0AAQHLAMUAAQHCAAMBAAHCAAMBAAHGAMIByQABAcoAAQHHAMYBAQDCAcIAwgHDAMkBwwABAcsAAQFAAgsEAAEAAcUAwgHFAMIBxAADAQABxQABAcUAAwEAAcUAwgHEAAEBwwABAcUAAQHEAAEBxAABAUACB8YBwwABAcIAAQHEAAEBxgABAcQAAwEAAcIAxAHFAJYAygMAAAAAAAAAAAAACAC4A8UAAQHCAAMBAAHCAAIBAMcBwgDDAcYAAQHGAMkBxgADAQABygABAcMAAQHDAAEBwwABAcIAxwHCAAEBxAABAcsAAQHCAAEBxQDCAcUAwgHDAMIBAgABxQABAcIAwwHCAAEBxQACAQDEAcQAAQHFAMsBxQABAcQAAQHIAEACD8YAAQHCAAEBwgADAQABxAABAcQAxQADAQABwwAFAQABAAHGAAEBxADCAcQAAQHKAAEByQDCAcUAAQHGAEACDAQAAQABxAABAcQAAQHKAAEBwwABAcUAwgHFAAIBAMMBBAABAAHFAAEBxQADAQABxQDCAcQAAQHDAAEBygABAckAAQHDAAEBygABAUACEMYAwgHDAAMBAAHJAMUAAwEAAcMABQEAAQABxgABAcYAAQHDAAEBxADNAcIAAwEAAcIAxwEBAM0BAgABwgDHAcIAAQHEAAEByQABAcQAAQHFAMIBxQBAAg/EAAMBAAHFAMIBxAABAcMAAQHKAAEBxwDNAQEAxgFAAhHEAMIBwwABAcIAxAHFAMUAAwEAAcMABQEAAQABxgDCAcUAAQHEAAEBxwAFAQABAAHFAAEBwgABAcQAAQHDAAEBwwABAccAAQHDAAEBxAADAQABxAABAcMAAQHJAAEBxQABAcUAwgHFAMIBxAADAQABxQDCAcQAAwEAAcUAwgHEAAEBxAABAckAAQHKAAEBxgABAcYAAQHFAAEBxgABAckAwgHDAAEBxgABAcQAxgABAcUAAQHCAAEBxgDCAcUAAQHEAAEBxQDCAcIAAQHCAMIBxgABAcQAAQHDAAEBwwABAccAAQHDAAEBwwABAcIAAQHEAAEBwwABAcgAAQHHAAEBwwABAcIAAQHDAAMBAAHDAAEBwwABAcMAAwEAAcQAAQHCAAEBwwADAQABxAABAcQAAQHJAAEBywABAcQAAQHHAMMBwwABAcYAAQHIAAEBwgABAcIAAwEAAcQAAQHEAMYAAQHFAAEBwgDHAcIAxQHGAAEBwgDCAcQAAQHEAMIBxAABAcMAAQHEAAEBwwABAccAAQHDAAEBwgABAcMAAQHEAAEBwgABAckAxgHDAMMBxADDAUACCQEAxAHEAMMBwwDEAcYAAQHIAAEBzADEAcUAwwHGAAEBxQABAcUAAQHCAAEBxAADAQABwgDEAcUAQAQAQAILxgDCAcIAAQHDAMIBxAABAcUAwwHDAAEBygDCAQIAAUAIAEADBkACEsUAwgHEAAEBQAMAxABADADFAMQBQBAAxgCXABUAAAD///8AAADAwMCAgIAAgAAAmADOAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAwMDAwMDAwOSAAAAAAAAALwAAAD+/wAAAwQDBAMEAwQABQAFZgkAAAEAAAABAAAABAMEAwQDBANOAAAAAAAAAAAAAAAAAAAAAgICAgICAgIPAFtOT1RFU11FRElUSU1QAQEBAQEBAQEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAAAAAABAQEBAQAAAAAAAAAAAAAAAAAAAAAAAAAAAQEBAQEdMB4gt3jDY4/1iZYkY7RmAAAAAQEBAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEBAAAAAAAAAAAAAAAAAAACAgICAAAAAAEAAAAAAAAA2OkHAAAAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAQEAAAAAAAAAAAAAAAAAAAAAAAAAAQAAAAEBAQFmCQAAAQAAAAEAAAAEAwQDAQAAAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAABPVEVTXUVESVRJTVABAQEBAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAQEBAQAAAAAAAAAAAAAAAAAAAAAAAAAA </filedata> </file> </object> </item>