rename and change xref path

Hi

I want to rename and change xref path. I always get unhandled error.

What am I doing wrong????

mojofddxr is array od filenames
Lxref is combobox

Code:

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Private Sub datoteke_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles datoteke.Click
        Dim myOFD As New OpenFileDialog("Select DWG", "", "dwg", "Select DWG", _
            OpenFileDialog.OpenFileDialogFlags.AllowMultiple)
        If myOFD.ShowDialog = System.Windows.Forms.DialogResult.OK Then
            mojofddxr = myOFD.GetFilenames
            For Each myFileName As String In mojofddxr
                'Debug.Print("***EXPORT FOR " & myFileName)
                Dim myDB As New Database(False, True)
                myDB.ReadDwgFile(myFileName, FileOpenMode.OpenForReadAndAllShare, True, "")
                Using mytrans As Transaction = myDB.TransactionManager.StartTransaction
                    For Each myBlockName As String In potrazixref(myDB)
                        'Debug.WriteLine(myBlockName)
                        If Lxref.Items.IndexOf(myBlockName) < 0 Then
                            Lxref.Items.Add(myBlockName)
                        End If

                        'If Lblokova.FindString("myBlockName") Then  Else Lblokova.Items.Add(myBlockName)
                    Next
                End Using
                myDB.Dispose()
            Next
        End If
    End Sub

Private Sub zamxref_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles zamxref.Click
        Dim myDB As New Database(False, True)
        Dim myOFD As New OpenFileDialog("Select DWG", "", "dwg", "Select DWG", 0)
        If myOFD.ShowDialog = System.Windows.Forms.DialogResult.OK Then
            mojofdxr = myOFD.Filename
            Label1.Text = "Odabrali ste datoteku " & mojofdxr & ".dwg"
        End If
    End Sub


 Private Sub izvrsi_zamjenu(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles zamjeni.Click
        For i As Integer = 0 To Lxref.SelectedItem.Count - 1
            Dim imexrefa As String = Lxref.SelectedValue.ToString
            For Each myFileName As String In mojofddxr

             
                Using myDB As New Database(False, True)

                    myDB.ReadDwgFile(mojofdxr, FileOpenMode.OpenForReadAndAllShare, True, "")
                    Using mytrans As Transaction = myDB.TransactionManager.StartTransaction
                        For Each myBlockName As String In potrazixref(myDB)
                            Using myBt As BlockTable = mytrans.GetObject(myDB.BlockTableId, OpenMode.ForRead)
                                If myBt.Has(myBlockName) And imexrefa = myBlockName Then
                                    Dim btrId As ObjectId = myBt(myBlockName)

                                    Using myBtr As BlockTableRecord = mytrans.GetObject(btrId, OpenMode.ForRead)
                                        myBtr.PathName = "./" & mojofdxr & ".dwg"
                                    End Using
                                End If
                            End Using

                        Next
                        mytrans.Commit()
                    End Using ' ' transaction
                    myDB.SaveAs(mojofdxr, DwgVersion.Current) '<-- 2009
                End Using ' ' myDB

            Next ' ' myFileName
        Next

    End Sub

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Please help