Run-time Error '13' : Type Mismatch

[IbrahimL]

Hello Everyone,
I have successfully created a login page for my Order Processing System. When I enter my Username and Password correctly it logs in successfully and moved onto my next form called 'frmWelcome'. However if I enter the incorrect Username and Password I get Error:

Run-time Error '13' : Type Mismatch

I have tried everything, anyone that can help me?

Here is my code :

Option Compare Database
Option Explicit
Private Sub Form_load()
'When the form loads the enter form will open
DoCmd.OpenForm "frmLogin"
End Sub
 
Private Sub cmdLogin_Click()
'The dlookup funtion allows the records to be searched within the required table
    If txtPassword.Value = DLookup("[Password]", "tblUsers", "[UserName]='" & txtUserName.Value & "'") Then
   'This is opening the main menu and then closing the form enter
   DoCmd.OpenForm "frmWelcome"
   DoCmd.Close acForm, "frmLogin"
   'txtusername.Value = Null
   'txtpassword.Value = Null
 ElseIf (txtUserName.Value) Then
    MsgBox "Enter Username and Password", vbCritical, "Error"
    txtPassword.Value = ""
    txtUserName.SetFocus
    ElseIf (txtPassword.Value) Then
    MsgBox "Enter password", vbCritical, "Error"
    txtPassword.SetFocus
 Else
   'If incorrect details are entered into any of the fields and enter is selected this would display an error message
   MsgBox "Log in details are incorrect, Please try again", vbCritical, "Error"
   'Both the fields would clear
   txtUserName.Value = Null
   txtPassword.Value = Null
   txtUserName.SetFocus
 
 End If
End Sub
 
Private Sub txtUserName_LostFocus()
    'after the user leaves the colour text box, convert the entered
    'colour to proper case, e.g. all words start with upper case letters
    txtUserName.Value = StrConv(txtUserName, vbProperCase)
End Sub
 
Private Sub cmdExit_Click()
 'This closes the forms down completely
 DoCmd.Quit
End Sub

[NeoPa]

Line #16 is checking a string as if it's a boolean (which it isn't). The code should probably compare the string with something but it isn't.

PS. Line #5 is entirely unnecessary.

Before I leave I will make the point that storing passwords in visible form in a table is quite insecure and always recommended against. It's also a bit more secure to use the name and password in the DLookup() call and ceck only that a record has been returned. That way the actual password isn't even seen in the code.

[zmbd]

Please do the following:
I have an idea as to what is happening at line 11 in that your DLOOKUP is returning an invalid result; however, you need to do the following to confirm

- In the VBA editor: {Ribbon:Debug:Compile}
Fix any bugs that show up and save... Run {Ribbon:Debug:Compile} until no errors are returned.

- Change your code in lines 9 and 10 of the posted From:

Private Sub cmdLogin_Click () 
'The dlookup funtion allows the 

to:

Private Sub cmdLogin_Click()
STOP
'The dlookup funtion allows the

Start your database... now [F8] thru the code and enter the wrong password... you'll see that you return a null.

You would have found this if you coded it like:

Private Sub cmdLogin_Click()
   'The dlookup funtion allows the records to be searched within the required table 
   '
   Dim z_str_userrecordlookup AS string
   '
   z_str_userrecordlookup = dLookup "[Password]", "tblUsers", "[UserName]='" & txtUserName.Value & "'")
   '
   If txtPassword.Value = z_str_userrecordlookup Then
      'This is opening the main menu and then closing the form enter
      DoCmd.OpenForm "frmWelcome"
      '(... remaining code ...)

you would have returned a null value to the z_str_userrecordlookup and errored on that line: DLookup Function

DLookup function evaluates expr against the entire domain. Any field that is included in criteria must also be a field in domain; otherwise, the DLookup function returns a Null (Null: A value you can enter in a field or use in expressions or queries to indicate missing or unknown data. In Visual Basic, the Null keyword indicates a Null value. Some fields, such as primary key fields, can't contain a Null value.)

Change line 7 in my code to read:
z_str_userrecordlookup = NZ(DLookup("[Password]", "tblUsers", "[UserName]='" & txtUserName.Value & "'"), 0) and you don't get the error.

It used to be taught in CompSci courses that all functions should be returned to a variable - in fact, that had to be done at one point in time. It is a sad fact that programmers now take shortcuts by placing functions within logic blocks as doing so makes the code harder to troubleshoot.

[NeoPa]

Z makes a good point about compiling the code. I shouldn't have overlooked that. Here are a few tips that should help - Before Posting (VBA or SQL) Code.

[ADezii]

There is another point that I feel is worth mentioning, and that is I strongly feel that Passwords should be Case Sensitive, namely:

Password <> PASSWORD
Password <> PassworD
PaSSword <> PaSsword
etc.
Password will only equal Password

The following Code will account for that if you wish to use it:

'***************************** Code intentionally omitted and modified *****************************
Dim z_str_userrecordlookup As String
 
z_str_userrecordlookup = DLookup("[Password]", "tblUsers", "[UserName]='" & Me![txtUserName] & "'")
 
If StrComp(z_str_userrecordlookup, Me![txtPassword], vbBinaryCompare) = 0 Then
  MsgBox "Passed Validation"
Else
  MsgBox "Does NOT Pass Validation"
End If
'***************************************************************************************************

[NeoPa]

That's a nuisance ADezii. I'd not noticed that before. That means putting an encrypted version of the password entered as part of the criteria won't be a reliable test, as SQL seems to compare/filter by letter rather than by case/binary.

Bearing in mind the more secure way of testing for passwords is storing them as encrypted values and never holding the actual password as text in your module, doing it properly would require that one used the technique you suggest with some standard (Used to store the data as well as check it) function procedure to encrypt / obscure the actual password value :

Dim strEncPW As String, strWhere As String
 
strWhere = Replace("[UserName]='%N'", "%N", Me.txtUserName)
strEncPW = DLookup("[Password]", "[tblUsers]", strWhere)
 
If StrComp(strEncPW, EncFunc(Me.txtPassword), vbBinaryCompare) = 0 Then
    'Passed Validation
Else
    'Did NOT Pass Validation
End If