Problems updating a datarow in sql

I am attempting to update a datarow in a sql database with a selected item in a ddl.  I am using the following code:

 Dim connectionstring As String = ("my connection")
        Dim query As String = ("Update properties Set available='@available' where ID='@ID'")
        Dim conn As New SqlConnection(my connection)
        Dim cmd As New SqlCommand(query, conn)
        cmd.Parameters.AddWithValue("@available", DropDownList4.SelectedItem)
        conn.Open()
        cmd.ExecuteNonQuery()
        conn.Close()
Basically, I want the person to be able to update that particular record.  When I run this application, this is the error I am getting:

System.ArgumentException: No mapping exists from object type System.Web.UI.WebControls.ListItem to a known managed provider native type.
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smitty68521Asked:
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Ryan ChongCommented:
try:

Dim query As String = ("Update properties Set available=@available where ID=@ID")

instead?

also, you need provide 2 parameters for the command object.
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smitty68521Author Commented:
I have tried that and I still get the same error. I see what you are saying as far as adding two parameters for the command object. However, I am not sure how to set the command parameter for the ID when it is simply a querystring I use from a previous page that dispays the data in the gridview.

I appreciate your help so far.
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Ryan ChongCommented:
try:

        Dim ID As String = ""
        If String.IsNullOrEmpty(Request.QueryString("ID")) = False Then
            ID = Request.QueryString("ID").ToString()
        Else
             'Or redirect or terminate process
        End If

'...

Dim connectionstring As String = ("my connection")
        Dim query As String = ("Update properties Set available=@available where ID=@ID")
        Dim conn As New SqlConnection(my connection)
        Dim cmd As New SqlCommand(query, conn)

        cmd.Parameters.AddWithValue("@available", DropDownList4.SelectedItem)
        cmd.Parameters.AddWithValue("@ID", ID)

        conn.Open()
        cmd.ExecuteNonQuery()
        conn.Close()
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smitty68521Author Commented:
This didn't work either. It doesn't give any errors this time but it also doesn't update the database. I will keep researching. I tried a request.querystring earlier but it didn't work either. Thanks for your help so far.
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Ryan ChongCommented:
it works for me, perhaps you can post a more complete scripts here?
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smitty68521Author Commented:
More complete? What I had in my first post was it. This is what is causing the error. It stops at "execute nonquery" I don't know what more I could provide you with. I am not sure what is going on with this. I have had projects similar to this and got them to work just fine. I appreciate your help so far though.
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Ryan ChongCommented:
try change:

DropDownList4.SelectedItem

to:

DropDownList4.SelectedItem.Value

?
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smitty68521Author Commented:
It worked! Thanks for your help. Great Expert.
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