Macro not run in Share Wrokbook

[Abdul Haneef]

I added some VBA code to a workbook. code specially doing protect the particular column if the date is less than current date. VBA codes work beautifully when the workbook is not shared.

When I share the workbook, then code will not work in shared mode. Error Msg is showing
"run time error '1004'
Unprotect method of worksheet class faild"

Code what i using below mention.

Private Sub Workbook_Open()
Const PC_ROW_DATE As Integer = 1

Worksheets("Sheet1").Unprotect
    
    Dim lngCol As Long
    
       For lngCol = 2 To Range("A" & PC_ROW_DATE).CurrentRegion.Columns.Count
        If Cells(PC_ROW_DATE, lngCol) < Date Then
            Columns(lngCol).Locked = 1
            Else
            Columns(lngCol).Locked = 0
        End If
    Next lngCol
    
 Worksheets("Sheet1").Protect 
End Sub

I just can't figure out why code doesn't work? please provide the help.