[AccessD] OpenArgs Issue...I think

I put out a report that uses OpenArgs to pass along the Beginning and Ending dates for a requested report. Here is the code that calls it...
 
DoCmd.OpenReport stDocName, acPreview, , , , txtBegDate.Value & "|" & txtEndDate.Value
 
And here is the code at the report end, OnOpen...
_________________________________________________________________________
Private Sub Report_Open(Cancel As Integer)
 
Dim aryOA As Variant
aryOA = Split(Me.OpenArgs, "|")
 
Me.lblBegDate.Caption = aryOA(0)
Me.lblEndDate.Caption = aryOA(1)
 
End Sub
_________________________________________________________________________
 
I was asked to do another report...on Voucher Number, instead of Date. I lacked forsight when I created this thing, and to make up for it, I figured starting and ending number would be the same as starting and ending date, and that is fine. But, for some reason, when I call the report for number, I get an error, "Invalid Use of Null" 
 
This error takes me to the OnOpen code above. 
 
I put in some test field, on the calling form, and verified that these number ARE going into the two values I am sending. 
 
Any ideas?
 

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