ASP.Net SqlDataSource parameter Error: Must declare the scalar variable

sir, 

on the last line Gridview1.databind() I am having error 

Must declare the scalar variable "@srname".

below is my code for asp.net vs2010 

Protected Sub CMDSEARCH_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles CMDSEARCH.Click, GridView1.PageIndexChanged
    Dim SqlDataSource1 As New SqlDataSource()
    Dim SQL As String
    ' If Not IsPostBack Then
    SqlDataSource1.ID = "sqlexpsearch"
    Me.Page.Controls.Add(SqlDataSource1)
    Dim connectionString As String
    Dim connection As SqlConnection
    connectionString = ConfigurationManager.ConnectionStrings("exam2ndconnection").ToString
    connection = New SqlConnection(connectionString)
    SqlDataSource1.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings("exam2ndconnection").ConnectionString
 
    If opname.Checked = True Then
        SQL = "select SRNO,tr_date as  Date ,MailMethod,SpeedId,Content,ExYear,Exroll as No,NAME,Address from dispatch where name = '%'+ @srname +'%' OR ADDRESS ='%'+ @srname +'%' order by TR_DAte DESC,NAME  "
        SqlDataSource1.SelectParameters.Add("@srname", UCase(txtitem.Text))
 
        SqlDataSource1.SelectCommand = SQL
    End If
    If opchno.Checked Then
        SqlDataSource1.SelectCommand = "select SRNO,tr_date as Date ,MailMethod,SpeedId,Content,ExYear,Exroll as No,NAME,Address from dispatch  where rtrim(exroll) ='" & txtitem.Text & "' order by tr_Date,exroll desc"
    End If
 
    GridView1.DataSource = SqlDataSource1
    GridView1.DataBind()
End Sub

Please guide how to solve it.