B4J Question B4XSerializator error

Sub AStream_NewData (Buffer() As Byte)
    Dim mm As MyMessage = ser.ConvertBytesToObject(Buffer)
End Sub

java.lang.RuntimeException: java.lang.ClassNotFoundException: b4j.example.showmain$_mymessage
    at anywheresoftware.b4a.randomaccessfile.B4XSerializator.readType(B4XSerializator.java:314)
    at anywheresoftware.b4a.randomaccessfile.B4XSerializator.readObject(B4XSerializator.java:374)
    at anywheresoftware.b4a.randomaccessfile.B4XSerializator.ReadObject(B4XSerializator.java:129)
    at anywheresoftware.b4a.randomaccessfile.B4XSerializator.ConvertBytesToObject(B4XSerializator.java:99)
    at b4j.example.show_digram._astream_newdata(show_digram.java:860)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at anywheresoftware.b4a.shell.Shell.runMethod(Shell.java:629)
    at anywheresoftware.b4a.shell.Shell.raiseEventImpl(Shell.java:234)
    at anywheresoftware.b4a.shell.Shell.raiseEvent(Shell.java:167)
    at jdk.internal.reflect.GeneratedMethodAccessor7.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at anywheresoftware.b4a.BA.raiseEvent2(BA.java:111)
    at anywheresoftware.b4a.shell.ShellBA.raiseEvent2(ShellBA.java:100)
    at anywheresoftware.b4a.BA$2.run(BA.java:250)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: java.lang.ClassNotFoundException: b4j.example.showmain$_mymessage
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:602)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
    at java.base/java.lang.Class.forName0(Native Method)
    at java.base/java.lang.Class.forName(Class.java:340)
    at anywheresoftware.b4a.randomaccessfile.RandomAccessFile.readTypeClass(RandomAccessFile.java:546)
    at anywheresoftware.b4a.randomaccessfile.B4XSerializator.readType(B4XSerializator.java:291)
    ... 24 more