SQLException Unhandled By User Code

Cannot insert the value NULL into column 'PortfolioID', table 'SazamaBuilders.dbo.Portfolio'; column does not allow nulls. INSERT fails.
The statement has been terminated.

 Looking for help with the correcting this.

This is the complete error message I am receiving. When debugging and I try to save something the error comes up right next to objportfolio.Save(). The following is my code for the save button:Protected Sub btnSave_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSave.Click

 

If Page.IsValid ThenDim objportfolio As New BusinessObjects.Portfolio

objportfolio.LoadByPrimaryKey(ViewState("ItemID"))

If objportfolio.es.HasData = False Then

objportfolio.AddNew()

End IfWith objportfolio

.portfolioName = Me.txtportfolioName.Text

' See if the directory is there, if not, create one

If IO.Directory.Exists(Server.MapPath("../Gallery/")) = False ThenIO.Directory.CreateDirectory(Server.MapPath("../Gallery/"))

End If

If Me.FileUpload1.HasFile ThenMe.FileUpload1.SaveAs(Server.MapPath("../Gallery/" & Me.FileUpload1.FileName))

.Filename = Me.FileUpload1.FileName

End If

End With

'Now save the portfolio

objportfolio.Save()

'Cleanup

objportfolio = NothingResponse.Redirect("./manage_portfolio.aspx")

End If

 

End Sub