Try this:

Private Sub CheckBox26_Click()
' This works as clear all for other checkboxes 1 t0 25
Dim k as integer
If CheckBox26.Value = False Then ' Checkbox26 is the control checkbox
to clear the other 25
For k = 1 To 25 ' check boxes 1 to 25
Me.Controls("Checkbox" & k).Value =' False set all boxes false
Next k
End If
End Sub