Chart problems....

[Goomba79]

Hello,

I have a few charts on my web form. they ar eall working apart from one!
my code thats populating the cart is as follows

Protected Sub ddlUserBm_SelectedIndexChanged(sender As Object, e As System.EventArgs) Handles ddlUserBm.SelectedIndexChanged

        Dim USerBM As String = ddlUserBm.SelectedValue

        con.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = ../SR.mdb"

        sql = "Select OpNumber, AVG(Competence) As AvgCompetence From Skills Where BMno = " & USerBM & " and EmpNo = " & Session("Employee") & " "

        DSstat = StatDC.SelectData(sql, con)


        chUserBM.Series("Series1").XValueMember = "OpNumber"
        chUserBM.Series("Series1").YValueMembers = "AVGCompetence"
        chUserBM.DataSource = DSstat
        chUserBM.DataBind()

    End Sub

when i selct an item in the list ddlUserBM

I get the following error pop up...

Line: 869

Error: Sys.WebForms.PageRequestManagerServerErrorException: No value given for one or more required parameters.)

If I tie a couple of labels to my vairables UserBM and session("employee") i get the correct text displayed

does anyone know why I am getting this problem???

it's been driving me crazy for ages!

thanks,

Iain