error in runtime with a crystal report and vb.net

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C#

VB

reporting

Hi After days of searching the web without success, I just explain my problem to get help. Thank you in advance.
I use VB 2008 + ACCESS 2007 with Crystal Reports for VS 2008, Windows 7.
Here is my problem: I am writing an application that manages the accounting ratios.
When I write a formula in the editor, CR does not report me any error (no error was found). But at runtime, I get the error "This field name is unknown"
The formula, written with Crystal syntax

if then {View_Etab_ParRatio.Seuil_Min}=0 then
   cstr ({View_Etab_ParRatio.Janvier}, 0)
else
   cstr ({View_Etab_ParRatio.Janvier}, 2)

curiously, when I simplify the formula by writing eg cstr({View_Etab_ParRatio.Janvier, 0), I do not get an error neither in the editor, nor at running time. Everything goes well.
I note that I call my report a datatable (MyPrintDatatable), which I create with a request
Here the lines of the report display

Dim MyCustomReport As SISCEC.rptView_Etab_ParRatio
MyCustomReport = New SISCEC. rptView_Etab_ParRatio
MyCustomReport.SetDataSource (MyPrintDatatable) 'load the source of the report
'Report display
frmPrint.crViewerDoc.ReportSource = MyCustomReport
frmPrint.ShowDialog ()

NB: The state was created in the design with the name query View_Etab_ParRatio

Thank you for your help