Problème de modification du type d'une colonne d'un fichier source Excel

#Region "Help: Introduction to the script task"
'The Script Task allows you to perform virtually any operation that can be accomplished in
'a .Net application within the context of an Integration Services control flow.
'Expand the other regions which have "Help" prefixes for examples of specific ways to use
'Integration Services features within this script task.
#End Region
#Region "Imports"
Imports System
Imports System.Data
Imports System.Math
Imports Microsoft.SqlServer.Dts.Runtime
Imports Microsoft.Office.Interop
#End Region
'ScriptMain is the entry point class of the script. Do not change the name, attributes,
'or parent of this class.
<Microsoft.SqlServer.Dts.Tasks.ScriptTask.SSISScriptTaskEntryPointAttribute()> _
<System.CLSCompliantAttribute(False)> _
Partial Public Class ScriptMain
    Inherits Microsoft.SqlServer.Dts.Tasks.ScriptTask.VSTARTScriptObjectModelBase
    Public Sub Main()
        Dim m_XlApp As New Excel.Application
        Dim m_xlWrkbs As Excel.Workbooks = m_XlApp.Workbooks
        Dim m_xlWrkb As Excel.Workbook
        m_xlWrkb = m_xlWrkbs.Open(Convert.ToString(Dts.Variables("User::ExcelPath").Value))
        Dim m_XlWrkSheet As Excel.Worksheet = m_xlWrkb.Worksheets(1)
       


        Dim c_bureau As Excel.Range
        Dim c_situation As Excel.Range
      

        With m_XlWrkSheet 
            c_bureau = m_XlWrkSheet.Cells.Find("bureau", LookIn:=Excel.XlFindLookIn.xlValues)          
            c_situation = m_XlWrkSheet.Cells.Find("situation", LookIn:=Excel.XlFindLookIn.xlValues)       

            If Not c_bureau Is Nothing Then               
                m_XlWrkSheet.Columns(c_bureau.Column).NumberFormat = "@"
                MsgBox("hello1")
                m_xlWrkb.Save()
            End If

            If Not c_situation Is Nothing Then               
                m_XlWrkSheet.Columns(c_situation.Column).NumberFormat = "@"
                MsgBox("hello2")
                m_xlWrkb.Save()
            End If      
           
            m_xlWrkb.Close(SaveChanges:=True)
        End With
        Dts.TaskResult = ScriptResults.Success
    End Sub
#Region "ScriptResults declaration"
    'This enum provides a convenient shorthand within the scope of this class for setting the
    'result of the script.
    'This code was generated automatically.
    Enum ScriptResults
        Success = Microsoft.SqlServer.Dts.Runtime.DTSExecResult.Success
        Failure = Microsoft.SqlServer.Dts.Runtime.DTSExecResult.Failure
    End Enum
#End Region
End Class