Run-time error '1004' Method 'Rows' of Object_Global failed

Hey !
I am writing VBA code for finding last_row of next sheet inside a chart sheet, in chart I a using Chart_MouseUp and Chart_MouseDown function here I am explaining Chart_MouseUp  inside  Chart_MouseDown event I am taking I am taking chart start point x and y co-ordinate and and on Chart_MouseUp  event I am taking chart end point x and y co-ordinate and after this process I am storing start point and end end point x co-ordinate inside next sheet "AQ" column for this purpose I have to know number of cell which is blanked inside AQ column for this I have to know last_Row of AQ cell and for this purpose I am using this code

                   Dim last_Row As Integer
                  last_Row = Sheets(5).Range("B" & Rows.count).End(xlUp).Row
                  MsgBox last_Row

 Run-time error '1004'
 Method 'Rows'  of Object_Global failed
Whenever code like

'Sheets(5).Range("AQ4") = startX
'Sheets(5).Range("AQ5") = endX is working inside same sheet

here is Chart_MouseUp event code Please I have an Idea to handle this problem then guide me

Dim startX as Long
Dim startY as String
Dim endX as Long
Dim endY as String

Private Sub Chart_MouseUp(ByVal Button As Long, ByVal Shift As Long, _
        ByVal x As Long, ByVal y As Long)

    Dim ElementID As Long, Arg1 As Long, Arg2 As Long
    Dim myX As Variant, myY As Double
    With ActiveChart
        ' Pass x & y, return ElementID and Args
        .GetChartElement x, y, ElementID, Arg1, Arg2
        ' Did we click over a point or data label?
        If ElementID = xlSeries Or ElementID = xlDataLabel Then
            If Arg2 > 0 Then
                ' Extract x value from array of x values
                myX = WorksheetFunction.Index _
                    (.SeriesCollection(Arg1).XValues, Arg2)
                ' Extract y value from array of y values
                myY = WorksheetFunction.Index _
                    (.SeriesCollection(Arg1).Values, Arg2)
                     endX = CDate(myX)
                     endY = myY
                   ' Display message box with point information
                     MsgBox "X = " & startX & vbCrLf _
                    & "Y = " & startY & vbCrLf _
                    & "X = " & endX & vbCrLf _
                    & "Y = " & endY
                    'Sheets(5).Range("AQ4") = startX
                    'Sheets(5).Range("AQ5") = endX
                    Dim last_Row As Integer
                    'Dim sh As Worksheet
                    last_Row = Sheets(5).Range("B" & Rows.count).End(xlUp).Row
                    MsgBox last_Row
                    
            End If
        End If
    End With
  
End Sub

And Chart_MouseDown event will be like this

Private Sub Chart_MouseDown(ByVal Button As Long, ByVal Shift As Long, _
        ByVal x As Long, ByVal y As Long)

    Dim ElementID As Long, Arg1 As Long, Arg2 As Long
    Dim myX As Variant, myY As Double
    With ActiveChart
        ' Pass x & y, return ElementID and Args
        .GetChartElement x, y, ElementID, Arg1, Arg2
        ' Did we click over a point or data label?
        If ElementID = xlSeries Or ElementID = xlDataLabel Then
            If Arg2 > 0 Then
                ' Extract x value from array of x values
                myX = WorksheetFunction.Index _
                    (.SeriesCollection(Arg1).XValues, Arg2)
                ' Extract y value from array of y values
                myY = WorksheetFunction.Index _
                    (.SeriesCollection(Arg1).Values, Arg2)
                     startX= CDate(myX)
                     startY= myY       
            End If
        End If
    End With 
End Sub
Note : At first Chart_MouseDown event occur then after Chart_MouseUp event will be occurred

Happy Coding !