i am fill datase with more than one Data Adapterit works fine with one and when the second fill method is executed i get a error "Object Instance is not Set to the Instance of the Object"

what can be wrong...

Code:
Public Ds_ORG As DataSet = New DataSet()

    Public Sub Init_DataSet()
        Try
            Dim OIT_User_SelectCmd As New SqlClient.SqlCommand("select * from OIT_User", Cn)
            Dim OIT_User_Adapter As SqlClient.SqlDataAdapter

            Dim OIT_Permissions_SelectCmd As New SqlClient.SqlCommand("select * from OIT_Permissions", Cn)
            Dim OIT_Permissions_Adapter As SqlClient.SqlDataAdapter

            Dim OIT_Folder_SelectCmd As New SqlClient.SqlCommand("select Rec_ID,Folder_Name,Folder_Parent,Folder_Type,Icon_rec_id,IsRecycle,Old_Parent_Folder,User_Created from OIT_FOLDER where (ISTEMPLATE<>1) ", Cn)
            Dim OIT_Folder_Adapter As New SqlClient.SqlDataAdapter()

            Dim OIT_File_SelectCmd As New SqlClient.SqlCommand("select Rec_Id  , File_Name ,Folder_Rec_ID, File_DateUploaded,File_DateLastOpened, File_DateDownloaded,File_Description,File_TotalBytes,File_UserUploaded from oit_file where IsRecycle=0", Cn)
            Dim OIT_File_Adapter As SqlClient.SqlDataAdapter

            OIT_Folder_Adapter.SelectCommand = OIT_Folder_SelectCmd
            OIT_Folder_Adapter.Fill(Ds_ORG, "OIT_Folder")

'-----------------problem area------------------
            OIT_File_Adapter.SelectCommand = OIT_File_SelectCmd
            OIT_File_Adapter.Fill(Ds_ORG, "(OIT_File)")

            'OIT_User_Adapter.SelectCommand = OIT_User_SelectCmd
            'OIT_User_Adapter.Fill(Ds_ORG, "OIT_User")

            'OIT_Permissions_Adapter.SelectCommand = OIT_Permissions_SelectCmd
            'OIT_Permissions_Adapter.Fill(Ds_ORG, "OIT_Permissions")

        Catch e As Exception
            MsgBox(e.Message)
        End Try
    End Sub