Try the following version of the Highlight_Control procedure. When calling it, you will need to include both the OptionButton and the Frame as parameters.

e.g.
VB Code:
  1. Private Sub OptionButton1_Click()
  2.     Highlight_Control Me.OptionButton1, Me.Frame1
  3. End Sub

Here's the revised procedure.
VB Code:
  1. Private Sub Highlight_Control(ByRef MarkControl As Control, ByRef OptFrame As Control)
  2. Dim cMyControl As Control
  3.    
  4.     If TypeName(OptFrame) <> "Frame" _
  5.     Or TypeName(MarkControl) <> "OptionButton" Then
  6.         Exit Sub
  7.     End If
  8.    
  9.     For Each cMyControl In OptFrame.Controls
  10.         If TypeName(cMyControl) = "OptionButton" Then
  11.  
  12.             With cMyControl
  13.                 .BackColor = 10931133
  14.                 .ForeColor = &H4080&
  15.             End With
  16.  
  17.         End If
  18.     Next cMyControl
  19.  
  20.     With MarkControl
  21.       .BackColor = &HC0FFFF
  22.       .ForeColor = &HFF0000
  23.     End With
  24.  
  25. End Sub