Hide sheet rows when ticking checkbox - debug error

I have inserted some code as below on a sheet in my workbook called "Implementation". When the checkbox is ticked it hides/unhides rows. It does this but also unfortunately it throws up a debug error which I can't seem to get rid of. Very frustrating! I had it working fine before when it was called "Sheet1" and I'm not a programmer so dunno what i'm doing really! I tried using "ActiveSheet" instead of Sheets("Implementation") too but the resulting error was the same. Help!

Private Sub CheckBox18_Click()

Rows("40:42").Select
If CheckBox18.Value = True Then
    Selection.EntireRow.Hidden = False
    Sheets("Implementation").CheckBox19.Visible = True
End If

If CheckBox18.Value = False Then
   Selection.EntireRow.Hidden = True
    Sheets("Implementation").CheckBox19.Visible = False
End If
    Range("$A$32").Select

End Sub

I've got rid of this error by using a workaround which means I don't have to address it now, however I have another problem... when I remove the ticks in all the checkboxes (which then hides rows), save and close the spreadsheet...... on reopening it I find that all the checkboxes have been resized (squashed or stretched) and in some cases disappeared entirely! I am sure they are there but they've probably been resized to zero width or something. Help?

I cant very easily do that without compromising my company confidentiality.

I thought of a workaround which would be to save it with all boxes checked and then run a macro on opening that just clears them all down. Not sure if this will work and not sure how to do it. Any suggestions?

ok so here is the sheet I am working ok. As you can see, when you click on the section headings it expands showing other tickboxes... they are fine if I save the sheet with all main sections ticked but if I save the file with them unticked (and therefore the sections collapsed) when I click the section headings to expand, the tickboxes are all messed up.