How do I debug a message if another message prevents me from doing so ?!?

[vodkasoda]

OK, a vague enough question I am sure, but this is my predicament :

If I run my VBA program I get an error message "Argument Not Optional" ... but if I debug I get the message "Can't execute code in break mode" !!

My main VBA is in Thisworkbook and the new code is as follows :

    Range("B11").Activate
    
    Set myRange1 = Range("B" & (10 + mySession))
    Set myRange2 = Range("H" & (10 + mySession))
    
    If myRange1 = "" Then
        Call StartBlink(myRange2)
    End If
        
    Application.ScreenUpdating = True

The Module Blinking_Text contains the following code (this is adapted from code I have found online, I am not sure what this RunWhen stuff does) :

Option Explicit
Public RunWhen As Double
 
Sub StartBlink(BlinkCell As Range)
    
    If BlinkCell.Font.ColorIndex = 1 Then
        BlinkCell.Font.ColorIndex = 2
    Else
        BlinkCell.Font.ColorIndex = 1
    End If
    
    RunWhen = Now + TimeSerial(0, 0, 1)
    
    Application.OnTime RunWhen, "StartBlink", , True
    
End Sub
 
Sub StopBlink(BlinkCell As Range)

    BlinkCell.Font.ColorIndex = xlAutomatic
    
    Application.OnTime RunWhen, "StartBlink", , False
    
End Sub

Any ideas ?