Clear userform if expiry date exceeds Today

Hi, attached is a file that we use to generate labels for our reagents. After selecting a reagent and the lot number, an expiry date is populated based on the data in the "Expiry" tab. What I hope to achieve is to have a popup msg appear when a user selects an expired chemical and the userform will clear so that the user can start again. Have tried some methods including addition of a textbox that shows today's date, but seems like im not getting it right.The textbox showing today's date can be removed if it is not required.

Here you go...just modified your cboLot event handler:

Private Sub cboLot_Change()
    Dim rng As Range
    Dim cell As Range
    
    Set sh = ThisWorkbook.Sheets("Expiry")
    Set rng = sh.Range("A2", sh.Cells(sh.Rows.Count, "A").End(xlUp))
    
    On Error Resume Next
    
    For Each cell In rng.Cells
        If cell.Value = Me.cboReagent.List(Me.cboReagent.ListIndex) Then
            If CStr(cell(1, 2).Value) = Me.cboLot.List(Me.cboLot.ListIndex) Then
                TextBox3.Value = cell(1, 3).Text
                g_Date_Expiry = cell(1, 3).Value
                If cell(1, 3).Value <= Date Then
                    MsgBox ("This lot expired. Please select different lot.")
                    Unload UserForm1
                    UserForm1.Show
                End If
                Exit Sub
            End If
        End If
    Next cell
End Sub

You may want to consider checking the expiry date when populating the Lot combobox and just omitting expired lots.

Private Sub cboReagent_Change()
    Dim cUnique As Collection
    Dim index As Integer
    index = cboReagent.ListIndex
    
    cboLot.Clear
    
    Dim rng As Range
    Dim cell As Range
    Dim vNum As Variant
    Dim sh As Worksheet
    
    Set sh = ThisWorkbook.Sheets("Expiry")
    
    'Extract unique chemical names from column A
    Set rng = sh.Range("A2", sh.Cells(sh.Rows.Count, "A").End(xlUp))
    Set cUnique = New Collection
    
    On Error Resume Next
    For Each cell In rng.Cells
        If cell.Value = Me.cboReagent.List(index) And cell.Offset(, 2).Value > Date Then
            cUnique.Add cell(1, 2).Value, CStr(cell(1, 2).Value)
        End If
    Next cell
    On Error GoTo 0
    If cUnique.Count = 0 Then cUnique.Add "No active lots available."
    
    For Each vNum In cUnique
        Me.cboLot.AddItem vNum
    Next vNum
    
    If cboReagent.Value = "Kastle Meyer Reagent" Or cboReagent.Value = "3% (w/w) Hydrogen Peroxide" Or cboReagent.Value = "Absolute Alcohol" Then
    cboName.Enabled = True
    TextBox2.Enabled = False
    Else
    cboName.Enabled = False
    TextBox2.Enabled = True
    End If

End Sub

You could also test the date when populating the