>Hello Everybody,
>
>I get the following error message when I try to run the following statement to Serialize data:
>
>

>oSoapFormatter.Serialize(oFileStream, oSoapFormatter)
>

>
>Type 'System.Runtime.Serialization.Formatters.Soap.SoapFormatter' in Assembly 'System.Runtime.Serialization.Formatters.Soap, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' is not marked as serializable.
>
>Here is the complete code:
>
>

>Imports System.IO
>Imports System.Runtime.Serialization
>Imports System.Runtime.Serialization.Formatters.Binary
>Imports System.Runtime.Serialization.Formatters.Soap
>Imports System.Reflection
>
>Public Class Form2
>
>    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
>
>        Dim oHashTable As New Hashtable
>
>        oHashTable.Add("One", 1)
>        oHashTable.Add("Two", 2)
>        oHashTable.Add("Three", 3)
>
>        SaveSoapData("C:\Users.XML", oHashTable)
>
>    End Sub
>
>    Sub SaveSoapData(ByVal sFilename As String, ByVal oObjectToSave As Object)
>
>        Try
>
>            Dim oFileStream As FileStream = New FileStream(sFilename, FileMode.Create)
>
>            Dim oSoapFormatter As New SoapFormatter(Nothing, New StreamingContext(StreamingContextStates.File))
>
>            oSoapFormatter.Serialize(oFileStream, oSoapFormatter)
>
>            oFileStream.Close()
>
>        Catch oError As Exception
>
>            Dim sErrorString As String
>            sErrorString = "Message ---" & oError.Message
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "HelpLink ---" & oError.HelpLink
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "Source ---" & oError.Source
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "StackTrace ---" & oError.StackTrace
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "TargetSite ---" & oError.TargetSite.ToString
>
>           MessageBox.Show(sErrorString, "Error")
>
>            End
>
>        End Try
>
>    End Sub
>
>    Function LoadSoapData(ByVal sFilename As String) As Object
>
>        Try
>
>            Dim oFileStream As FileStream = New FileStream(sFilename, FileMode.Open)
>
>            Dim oSoapFormatter As New SoapFormatter(Nothing, New StreamingContext(StreamingContextStates.File))
>
>            LoadSoapData = oSoapFormatter.Deserialize(oFileStream)
>
>            oFileStream.Close()
>
>        Catch oError As Exception
>
>            Dim sErrorString As String
>            sErrorString = "Message ---" & oError.Message
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "HelpLink ---" & oError.HelpLink
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "Source ---" & oError.Source
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "StackTrace ---" & oError.StackTrace
>            sErrorString = sErrorString & vbCrLf
>            sErrorString = sErrorString & "TargetSite ---" & oError.TargetSite.ToString
>            MessageBox.Show(sErrorString, "Error")
>
>            End
>
>        End Try
>
>    End Function
>
>End Class
>

I think you want to change the line

oSoapFormatter.Serialize(oFileStream, oSoapFormatter)

to

oSoapFormatter.Serialize(oFileStream, oObjectToSave)

Also, note in the remarks section at http://msdn.microsoft.com/en-us/library/system.runtime.serialization.formatters.soap.soapformatter%28v=vs.110%29.aspx that SoapFormatter is obsolete and it is suggested that you use BinaryFormatter instead.