Excel VBA validation errors when a spreadsheet is proteced

I'm trying to ensure that data entered into the named range of an Excel spreadsheet is valid. To do this, I've defined a static validation list for column "A" in the range, and enabled the dropdown list for that column. Based on the option selected by the user, I add a validation object in column "B" at runtime, having a list of entries constrained by the entry in column "A". Based on the entries in columns A and B, the cell in column "C" is automatically populated.

This works fine until spreadsheet protection is enabled. At that point, attempting to select an option from the droplist in column "B" generates the following error:

"The cell or chart that you are trying to change is protected and therefore read-only. ... "

However

• All cells in the range in question were unlocked prior to adding worksheet protection.
• The code explicitly removes protection prior to updating the validation object in column "B", then replaces it once the validation object has been added.
• When a list item is selected from the droplist in column "B", the error message fires immediately before any worksheet events occur, making it impossible to trap or debug the error.

I have code in both the spreadsheet and in a separate code module, both or which are included below. Any ideas would be greatly appreciated

Here's the code in the Worksheet_Change() event:

Private Sub Worksheet_Change(ByVal Target As Range)
   Dim strNm As String

  ' there will be multiple named ranges eventually. We need to be able to distinguish
  ' among the various ranges so that our code executes only against the data we expect
  ' to manipulate - not random cells
  If Not Intersect(ActiveCell, ActiveWorkbook.Names("DBAddRange").RefersToRange) Is Nothing Then  
     Dim rng As Range

     Set rng = ActiveWorkbook.Names("DBAddRange").RefersToRange

     If Target.Column = 1 Then
        If FLAG_CHANGE_IN_PROGRESS = True Then Exit Sub
        FLAG_CHANGE_IN_PROGRESS = True
        Dim VldnList As String

        VldnList = getVldtnList(Target.Value)

        unlockSS ActiveSheet
        Range("B" & Target.row).Clear
        Range("B" & Target.row).Select
        With Range("B" & Target.row).Validation
           .Delete
           .Add Type:=xlValidateList, Operator:=xlValidateList, Formula1:=VldnList
           .IgnoreBlank = False
           .InCellDropdown = True
        End With

        lockSS ActiveSheet
        Range("B" & Target.row).Select
        FLAG_CHANGE_IN_PROGRESS = False
     ElseIf Target.Column = 2 Then
        If FLAG_CHANGE_IN_PROGRESS = True Then Exit Sub
           FLAG_CHANGE_IN_PROGRESS = True
           unlockSS ActiveSheet
           Dim dbHost As Variant
           Dim hNmRng As Range
           Set hNmRng = ActiveWorkbook.Names("valid_lookups").RefersToRange
         dbHost = Application.VLookup(Target.Value, hNmRng, 2, False)

         Range("C" & Target.row).Value = dbHost
         lockSS ActiveSheet
         FLAG_CHANGE_IN_PROGRESS = False
      End If
   End If

   If Not Intersect(ActiveCell, ActiveWorkbook.Names("HostAddRange").RefersToRange) Is Nothing Then

   End If
End Sub

Code in the external module:

Sub lockSS(ByVal sheet As Sheet1)
   sheet.Protect Password:=[NOT SHOWN], UserInterfaceOnly:=True, DrawingObjects:=False
   Application.EnableEvents = True
End Sub

Function getVldtnList(ByVal dbName As String)
   Dim vrtmatchRow As Variant
   Dim rng As Range

   If dbName = "" Then
      getVldtnList = ""
      Exit Function
   End If

   ' this is a pre-defined range having entries for:
   ' DB Name   - Column 1
   ' DB CI ID  - Column 2
   ' DB Host   - Column 3

   Set rng = ActiveWorkbook.Names("valid_db_nms").RefersToRange

   ' find the value of the first row in the range that matches the value
   ' of the dbName parm. NOTE: the final 0 parm tells the match function
   ' to find an exact match.
   vrtmatchRow = Application.Match(dbName, rng, 0)

   If IsError(vrtmatchRow) Then
      ' NOTE: we should NEVER get here due to the way cell validation is set up.
      MsgBox "The value entered was not found in the list of valid database values. See xxx for help", vbRetryCancel, "Invalid Entry"
   Else
      Dim row As Long
      Dim strListVals As String

      Set rng = ActiveWorkbook.Names("valid_db_info").RefersToRange
      row = vrtmatchRow

      Do
         If Len(strListVals) > 0 Then strListVals = strListVals + ","
         strListVals = strListVals + rng.Cells(row, 2).Value
         row = row + 1
      Loop While (rng.Cells(row, 1).Value = dbName)
   End If

   getVldtnList = strListVals
End Function

Sub unlockSS(ByVal sheet As Sheet1)
   sheet.Unprotect Password:=[NOT SHOWN]
   Application.EnableEvents = False
End Sub