select multiple values from a cell data validation list dropdown

Hi all,

I would like to be able to select multiple values from a cell data validation list dropdown which are then entered into the cell within the chosen column. This is the code I have come up with which works but it sometimes gets a runtime error and disables the code which then requires me to re-open the spreadsheet to get it working again. I welcome any ideas on how to prevent this in my code.

Private Sub Worksheet_Change(ByVal Target As Range)

    Dim oldVal As String
    Dim newVal As String
    Dim sComments As String

    If Target.Count > 1 Then Exit Sub
    If Target.Column = 10 Then
    
  On Error GoTo exit_Click_Err

    'If Target.Column <> 100 Then
        newVal = Target.Value
        If newVal <> "" Then
            Application.EnableEvents = False
            Application.Undo

            Else
            End If
                
            oldVal = Target.Value
            If InStr(oldVal, newVal) = 0 Then
                Target.Value = IIf(oldVal = "", "", oldVal) & ";" & newVal
            End If
            Application.EnableEvents = True
        End If
        
exit_Click_Exit:
    Exit Sub

exit_Click_Err:
    'MsgBox Error$
    Resume exit_Click_Exit
         
    End Sub

For Info, the error normally occurs when I select the cell and hit delete key to delete any entries I have made and the error is : runtime error 1004 , method 'UNDO' of object '_Application failed'


Thanks

Skoolz