When I remove data, code will stuck - vba

Question

I have excel sheet with dropdown list and when I choose anything from the list
macro will vlookup for requested value. But when I want to remove values from those cells, that I select them and press delete, it will show me "#N/A" and the excel is frozen, I cant do anything. Could you advise me, how can I avoid it, please?
Option Explicit
Private Sub Worksheet_Change()
Dim Target As Range
Dim selectedNa As Integer, selectedNum As Integer
selectedNa = Target.Value
If Target.Column = 10 Then
selectedNum = Application.VLookup(selectedNa, ActiveSheet.Range("dropdown"), 2, False)
If Not IsError(selectedNum) Then
Target.Value = selectedNum
Else: Exit Sub
End If
Else: Exit Sub
End If
End Sub

Answer 1

Try the following:
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Dim selectedNa As Long, selectedNum As Variant
If Target.Column = 10 And Not IsEmpty(Target) Then 'selectedNa <> vbNullString Then '
Application.EnableEvents = False
On Error GoTo errhand
selectedNa = Target.Value
selectedNum = Application.VLookup(selectedNa, ActiveSheet.Range("dropdown"), 2, False)
If Not IsError(selectedNum) Then
Target.Value = selectedNum
End If
Application.EnableEvents = True
End If
Exit Sub
errhand:
If Err.Number <> 0 Then
Application.EnableEvents = True
End If
End Sub

Answer 2

Change your posted code to
Option Explicit
Private Sub Worksheet_Change(ByVal target As Range)
Dim selectedNa As Integer, selectedNum As Integer
On Error GoTo EH
Application.EnableEvents = False
selectedNa = target.Value
If target.Column = 10 Then
selectedNum = Application.VLookup(selectedNa, ActiveSheet.Range("dropdown"), 2, False)
If Not IsError(selectedNum) Then
target.Value = selectedNum
End If
End If
EH:
Application.EnableEvents = True
Debug.Print Err.Number, Err.Description
End Sub
The code HAS TO be put into the sheet module.
Have a look at the immediate window after you have changed or deleted a value in your sheet.

Answer 3

It looks like this is what you want, based on the information provided:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim CheckCells As Range
Dim ChangedCell As Range
Set CheckCells = Intersect(Me.Columns(10), Target)
Application.EnableEvents = False
If Not CheckCells Is Nothing Then
For Each ChangedCell In CheckCells.Cells
If Len(ChangedCell.Value) > 0 And WorksheetFunction.CountIf(Me.Range("dropdown"), ChangedCell.Value) > 0 Then
ChangedCell.Value = WorksheetFunction.VLookup(ChangedCell.Value, Me.Range("dropdown").Resize(, 2), 2, False)
End If
Next ChangedCell
End If
Application.EnableEvents = True
End Sub