Can't seem to insert a guid (userID) into table!

I'm creating a web project for one of my uni modules using Visual studio 2010. I'm using asp.net membership and have all of my sql-server tables set up correctly (I'm pretty sure).

I have a form that I have created myself that inserts into the database using sqlDataSource.insert(). I had some problems initially with not being able to insert any data into the table at all, but I have cleared that up.

My problem now is that I need to insert the currently logged in user's userID into one of the columns of the table. But every time I hit the submit button, I am told I cannot insert null values in the userID column.

I can retrieve the userID using this snippet:

    Dim userID As String
    Dim memUser As MembershipUser
    memUser = Membership.GetUser()
    userID = memUser.ProviderUserKey.ToString()
    e.Command.Parameters(0).Value = userID

This is the code behind for the page:

Public Class WebForm1
Inherits System.Web.UI.Page

'Dim userID As Guid = CType(memUser.ProviderUserKey, Guid)



Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    'Dim UserID As Guid = CType(Membership.GetUser.ProviderUserKey, Guid)
    'memUser = Membership.GetUser()
    Dim userID As Guid


    Dim memUser As MembershipUser
    memUser = Membership.GetUser()
    userID = memUser.ProviderUserKey

    If IsPostBack() Then
        Session.Add("UserID", userID)
    Else
        userID = Session("UserID")
    End If

    TextBox1.Text = userID.ToString


End Sub
Protected Sub SqlDataSource1_Selecting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.SqlDataSourceSelectingEventArgs) Handles SqlDataSource1.Selecting
    e.Command.Parameters(0).Value = userID

End Sub
Protected Sub buttonInsertCitation_Click(ByVal sender As Object, ByVal e As EventArgs) Handles buttonInsertCitation.Click


    SqlDataSou开发者_Go百科rce1.Insert()
End Sub
End Class

As you can see it is a bit of a mess, I've been frantically trying different variations, as I need to catch up a little with other uni modules.

Here is my SQLDataSource from the .aspx page, The controlparameters work fine for the other data I am inserting. maybe the <asp:parameter name="userID" /> is wrong?

<InsertParameters>
        <asp:parameter name="userID" />
        <asp:ControlParameter ControlID="textNotes" Name="notes" PropertyName="Text" />
        <asp:ControlParameter ControlID="textEssayTitle" Name="essayTitle" PropertyName="Text" />
        <asp:ControlParameter ControlID="radioIsPrivate" Name="isPrivate" PropertyName="Text" />
        <asp:ControlParameter ControlID="dropPaperID" Name="paperID" PropertyName="Text" />
</InsertParameters>

I'm relatively new to vb, and I come from a html & css background.

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With the ASP.NET membership providers, you don't need to worry about performing any sql.