Setting numeric format for a report field dynamically using VB .NET 4.0

I am trying to set the ThousandsSeparator value dynamically in a VB program.

Using VS 2012 with CR 13.0.2 (x64). 

Target CPU is x64

Ludek Uher provided an excellent post (http://scn.sap.com/thread/2083873) for a C# implementation.  However, my VB program fails when it tries to assign/cast the ISCRReportObject to the ISCRFieldObject.

The C# code in the post is:

ISCRFieldObject oldFieldObject = (ISCRFieldObject)reportObject;

In my VB program I have tried multiple ways to perform this assignment:

Dim reportObject   As CrystalDecisions.ReportAppServer.ReportDefModel.ISCRReportObject
Dim oldFieldObject As CrystalDecisions.ReportAppServer.ReportDefModel.ISCRFieldObject

reportObject = oldAllReportObjects("txtUpperAlertOut")
'at this point reportObject has the correct item from the report

'The following are 2 ways I tried to assign reportObject to oldFieldObject, both fail at run time
'-----------------------------------------------------------------------------------------------------------------------

oldFieldObject = reportObject

oldFieldObject = CType(reportObject, CrystalDecisions.ReportAppServer.ReportDefModel.ISCRFieldObject)

Any suggestions?

Thanks.