Validation code with Protected sheet

[sandu1]

Hello Guys,

I am using this code to filter out one of the drop down list based on cell entry and I have to protect the sheet post which this code doesnt seem to work, please help.
I tried unprotect and protect password in the code but that doesn't seems to work. Rest all other sheets with other codes are working fine.

Private Sub Worksheet_Change(ByVal Target As Range)
  Dim str1 As String
  If Target.Address(0, 0) = "K10" Then
     Range("B5").ClearContents
     On Error Resume Next
        Range("B5").Validation.Delete
     On Error GoTo 0
     str1 = LCase(Target.Value)
     If InStr(1, str1, "@gmail.com") Then
        Range("B5").Validation.Add Type:=xlValidateList, Formula1:="=vld_gmail"
     ElseIf InStr(1, str1, "hotmail.com") Then
        Range("B5").Validation.Add Type:=xlValidateList, Formula1:="=vld_hotmail"
     Else
        Range("B5").Validation.Add Type:=xlValidateList, Formula1:="=vld_all"
     End If
  End If
End Sub

Please help