Object reference not set to an instance of an object. Table not found in the report not exist in th

Magezi Sagesse

I have a form in Vb.net on which I put three different report object(chronoT,chronoAu,controleMois) and on previewcontrol in which I load those reports. For switching between those report I have a combobox that has 3 option; depending on what the user will choose in the combobox I load the corresponding report object in the previewcontrol.

The first report has two tables (chronogrammeTaches,synthesetaches),the second report has two tables also(chronoautre et syntheseautre) and the third has one table(controletachemois). I pass a custom sql command to fill those tables. to pass that custom sql command, I creat tabledatasource type variables that i refer to those report data tables and I load them in the preview control in three different procedure,here is how I do:

For the first report object in the procedure called chargerchronoObje:

dim tfiche as new tabledatasource,synthese as new tabledatasource
  tfiche = CType(chronoT.GetDataSource("ChronogrammeTache"), TableDataSource)
        synthese = CType(chronoT.GetDataSource("synthesertaches"), TableDataSource)
'Passing the custom sql command

 tfiche.SelectCommand = "SELECT DISTINCT taches.codet,taches.type,taches.tache,lignes.mois,lignes.coutu,lignes.annee FROM Taches INNER JOIN (RelierT INNER JOIN lignes  ON RelierT.codet = lignes.codet) ON taches.codet=RelierT.codet WHERE codep=a AND lignes.annee=b;"
  synthese.SelectCommand = "SELECT synthese.type, synthese.mois, synthese.annee, synthese.designationT, Count(synthese.codet) AS nbre, synthese.codea " & _
    "FROM (SELECT DISTINCT Taches.type, lignes.mois, Taches.codet, Taches.designationT, Taches.codea, lignes.annee " & _
    "FROM Taches INNER JOIN (RelierT INNER JOIN lignes ON RelierT.codet = lignes.codet) ON Taches.codet = RelierT.codet " & _
    "WHERE ((((Taches.codep)=a) AND (lignes.annee)=b)))  AS synthese GROUP BY synthese.type, synthese.mois, synthese.annee, synthese.designationT, synthese.codea;"

For the second in the procedure called chargerchronotache:

      dim tfiche1 as new tabledatasource, synthese1 as new tabledatasource
        tfiche1 = CType(chronoAu.GetDataSource("chronoautre"), TableDataSource)
        synthese1 = CType(chronoAu.GetDataSource("syntheseautre"), TableDataSource)
'Passing the custom sql command
 tfiche1.SelectCommand = "SELECT DISTINCT Specifiques.codes as codet,specifiques.codeG as codea,specifiques.specifique as tache, lignes.mois, 1 AS coutu,    lignes.annee FROM Specifiques INNER JOIN (activites INNER JOIN (Taches  INNER JOIN lignes ON taches.codet=lignes.codet) ON activites.codea=Taches.codea) ON specifiques.codes=activites.codes WHERE specifiques.codep=a AND lignes.annee=b"
   synthese1.SelectCommand = "SELECT Count(synthese.codet) AS Nbre,synthese.codea,synthese.mois, synthese.annee FROM (SELECT DISTINCT Specifiques.codes as codet,specifiques.codeG as codea,specifiques.specifique as tache, lignes.mois, 1 AS coutu, lignes.annee" & _
" FROM Specifiques INNER JOIN (activites INNER JOIN (Taches  INNER JOIN lignes ON taches.codet=lignes.codet) ON activites.codea=Taches.codea) ON specifiques.codes=activites.codes " & _
" WHERE activites.codep=a AND  lignes.annee=b) as synthese GROUP BY  synthese.codea,  synthese.mois, synthese.annee;"

For the third in the procedure called chargerControletache:

dim table As New TableDataSource
        table = CType(controleMois.GetDataSource("controletachemois"), TableDataSource)

'Passing custom sql command
 table.SelectCommand = "SELECT resume.codet, resume.type, resume.mois, resume.prevu, resume.realise AS realiser,(resume.prevu-resume.realise) AS ecart, ((([resume].[prevu]-[resume].[realise])*100)/[resume].[prevu]) AS ecartp, resume.annee FROM (SELECT synth.codet,synthe.type, synth.cout AS prevu, synth.mois, synth.annee, synthe.realise" & _
" FROM (SELECT lignes.codet,(lignes.coutu*lignes.frequence) as cout,lignes.mois,lignes.annee FROM lignes)  AS synth INNER JOIN (SELECT RelierT.codets as codet,lignes.mois,taches.type,SUM( IIf(IsNull([realisations.montantr]),0,[realisations.montantr])) AS realise, lignes.annee FROM RelierT INNER JOIN (taches INNER JOIN (lignes LEFT JOIN realisations ON lignes.ligne=realisations.ligne) ON taches.codet=lignes.codet) ON RelierT.codet=taches.codet WHERE taches.codep=a AND lignes.annee=b GROUP BY RelierT.codets,lignes.mois,type,lignes.annee)  AS synthe ON synth.codet = synthe.codet AND synth.mois=synthe.mois AND synth.annee=synthe.annee " & _
"GROUP BY synth.codet, synth.cout, synth.mois, synth.annee, synthe.realise,synthe.type) As resume"

When I load for the first time those report inside the previewcontrol by calling their respective procedure one after another; they are loaded well, THE PROBLEM IS when I load for the second time on of these reports after another one by calling its procedure; for example for the third report : the expression

table = CType(controleMois.GetDataSource("controletachemois"), TableDataSource)

sets the table to nothing or null (C#) to mean that the table controletachemois does'nt exist in the report object controleMois; I get an exception that says the reference not set to an instance of an object Unless l I close and reopen again the form and load it for the first time.

I don't understand what is wrong, I've tried all I can but nothing is resolved. Can someone assist me please!!!!!!