Handling incorrect password runtime errors - excel

Question

First time post but a long time user! Firstly I wanted to say thank you to every for all the code feedback you guys put on posts. It's helped me develop my VBA code more than you can imagine!
Ok so the question:
Background:
I'm developing a VBA focused addin for myself and colleagues to use. Part of this is include functions that you would except in Excel but aren't there. Some of these were quite easy to do (ie invert filters) but some are proving more difficult. This is one of those examples.
Issue:
The following code is meant to loop through the users selection of sheets, apply a user defined password or remove the existing one. Part of the function is to capture passwords that can't be removed (ie becuase the user entered an incorrect password). It works great for the first error occurrence but throughs up the runtime error (1004) for the second and repeating ones after. I don't much much experience with runtime errors handling (try to avoid errors!) but I can't get this to work. Any ideas /help to stop the runtime error popping up would be great.
Code:
Dim SHT As Worksheet, Password As String, SHT_Names(0 To 30) As String
'PREP
'DISABLE APPLICATION FUNCTIONS
Call Quicker_VBA(False)
Application.EnableEvents = False
'USER PASSWORD OPTION
Password = InputBox("Please enter a password (leave blank for no password)", "Password")
'USER INFORMATION MESSAGES SETUP
MSG_Protect = "Added to-"
Protect_check = MSG_Protect
MSG_Unprotect = "Removed from-"
Unprotect_check = MSG_Unprotect
MSG_unable = "Unable to remove protection from-"
Unable_check = MSG_unable
'ID SHEETS SELECTED
For Each SHT In ActiveWindow.SelectedSheets
a = a + 1
SHT.Activate
SHT_Names(a) = SHT.name
Next
'MAIN
HomeSHT = ActiveSheet.name
'PROTECT SHEETS SELECTED BY USER
For b = 1 To a
Sheets(SHT_Names(b)).Select
Set SHT = ActiveSheet
'ENABLE OR REMOVE PROTECTION FROM SELECTED SHEET
If SHT.ProtectContents Then
On Error GoTo Password_FAIL
Application.DisplayAlerts = False
SHT.Unprotect Password
On Error GoTo 0
MSG_Unprotect = MSG_Unprotect & vbNewLine & Chr(149) & " " & SHT.name
Else:
'ENABLE FILTER CHECK
FilterOn = False
If ActiveSheet.AutoFilterMode Then FilterOn = True
'PROTECT SHEET
SHT.Protect Password, AllowFiltering:=FilterOn
'UPDATE USER MESSAGE
MSG_Protect = MSG_Protect & vbNewLine & Chr(149) & " " & SHT.name & " - Users can: Select locked and unlocked cells"
If FilterOn = True Then MSG_Protect = MSG_Protect & " and use filters"
End If
200 Next
'INFORM USER
If Protect_check <> MSG_Protect Then msg = MSG_Protect & vbNewLine & "___________________" & vbNewLine
If Unprotect_check <> MSG_Unprotect Then msg = msg & MSG_Unprotect & vbNewLine & "___________________" & vbNewLine
If Unable_check <> MSG_unable Then msg = msg & MSG_unable
MsgBox msg, , "Protection summary"
'TIDY UP
Sheets(HomeSHT).Activate
'ENABLE APPLICATION FUNCTIONS
Call Quicker_VBA(True)
Exit Sub
Password_FAIL:
MSG_unable = MSG_unable & vbNewLine & Chr(149) & " " & SHT.name
Application.EnableEvents = False
GoTo 200
End Sub

Answer 1

At a quick glance, it seems that the problem is in the way you're handling your errors. You use the line On Error GoTo Password_FAIL to jump down to the error handler. The error handler logs some information and then jumps up to label '200'. I can't tell if the formatting is off, but it looks like the label for '200' points to Next, indicating that the loop should continue with the next sheet.
So, where's the problem? You never actually reset the original error. Three lines below On Error GoTo Password_FAIL you explicitly call On Error GoTo 0 to reset the error handler, but that line will never actually be reached in an error. The program will jump to the error handler, and then from there jump up to the loop iterator. Using the GoTo statement for control flow can easily lead to these types of issues, which is why most developers recommend against it.
I'll post some sample code below to show a different (potentially better) way to handle code exceptions. In the sample below, the code simply loops through all of the worksheets in the workbook and toggles the protection. I didn't include much of your logging, or the constraint that only the selected sheets be toggled. I wanted to focus on the error handling instead. Besides, from reading you code, it seems that you can manage more of the peripheral details. Send a message if there's still some confusion
Sub ToggleProtectionAllSheets()
Dim sht As Worksheet
Dim password As String
On Error Resume Next
password = InputBox("Please enter a password (leave blank for no password)", "Password")
For Each sht In ActiveWorkbook.Worksheets
If sht.ProtectContents Then
sht.Unprotect password
If Err.Number <> 0 Then
Err.Clear
MsgBox "Something did not work according to plan unprotecting the sheet"
End If
Else
sht.Protect password
If Err.Number <> 0 Then
Err.Clear
MsgBox "Something went wrong with protection"
End If
End If
Next sht
End Sub