Run-time error '2501': The OpenForm action was canceled (Access 2010)

[Vodi]

I've looked through other related threads and can't find anything that works for my issue. I'm also an amateur in Access.

Here's how this database in Access 2010 works: A user opens the database and is greeted by a login form (frmLogin). They select their credentials from the dropdown list (cboUser) and type their password into the text box (txtPassword) and press Enter. frmLogin minimizes and frmMainMenu opens and takes the helm. frmMainMenu takes the user's credentials from frmLogin and displays their name on frmMainMenu. Each user is also assigned an access level to determine what forms/subforms they can edit. From frmMainMenu, the user can view various reports or open a form to input data.



The problem that I'm having is this Run-time error '2501'. It suddenly came up today and prevents users from logging in. I haven't changed anything in weeks and users can only input data through a form. Does anyone have any insight as to what may be causing this? Below is the code that comes up in the debugger (DoCmd.OpenForm "frmMainMenu" is highlighted yellow in the debugger):

Private Sub txtPassword_AfterUpdate()
If IsNull(Me.cboUser) Then
    MsgBox "Please select a User", vbCritical
    Me.cboUser.SetFocus
Else
    If Me.txtPassword = Me.cboUser.Column(2) Then
        If Me.cboUser.Column(3) Then
            DoCmd.OpenForm "frmPasswordChange", , , "[UserID] = " & Me.cboUser
        End If
        DoCmd.OpenForm "frmMainMenu"
Me.Visible = False
    Else
        MsgBox "Password does not match.  Please re-enter your password", vbOKOnly + vbExclamation
        Me.txtPassword = Null
        Me.txtPassword.SetFocus
    End If
End If
End Sub

Your time and assistance are much appreciated.

[June7]

If you are positive nothing has changed since the last successful login, only thing I can imagine is form corruption.

Probably should open frmPasswordChange in acDialog mode so the code execution will suspend until the form closes.