Error:input string was not in a correct format

[shervinrv]

Hello.
i have a autocompletebox . when i type a character i get this error : input string was not in a correct format

<telerik:RadAutoCompleteBox ID="acpstudents" Runat="server" DataSourceID="st" DataTextField="name" DataValueField="id" InputType="Text" MaxResultCount="10">
          </telerik:RadAutoCompleteBox>
          <asp:SqlDataSource ID="st" runat="server" ConnectionString="<%$ ConnectionStrings:dbconnection %>" EnableCaching="true" SelectCommand="SELECT [name]+' '+[lname] as name,[lname],[scode],[codemelli],[id] FROM [students] WHERE ([schoolid] = @schoolid)" SelectCommandType="Text">
              <SelectParameters>
                  <asp:CookieParameter CookieName="schoolmanager" Name="schoolid" Type="Int32" />
              </SelectParameters>
          </asp:SqlDataSource>

Thank You