Ambiguous Column Name Problem

I have a problem when running the code after I select an item from the dropdownbox and click select:
 1 <%@ Page Language="C#" MasterPageFile="~/Default.master" Title="View Orders allocated to Ships" %>
2 <%@ import namespace="System.Data.SqlClient" %>
3
4 <script runat="server">
5
6 protected void ShipIDSelect_Click(object sender, EventArgs e)
7 {
8 SqlConnection conn;
9 SqlCommand comm;
10 SqlDataReader reader;
11 string connectionString =
12 ConfigurationManager.ConnectionStrings[
13 "ShippingSystemConnectionString1"].ConnectionString;
14 conn = new SqlConnection(connectionString);
15 comm = new SqlCommand(
16 "SELECT OrderID, CustomerID, Date, NumberofItems, DescriptionsofItems, SafeItems, Destination FROM [Order] o, Ordersonship os " +
17 "WHERE os.ShipID = @ShipIDDropDownList " +
18 "AND o.OrderID = os.OrderID", conn);
19 comm.Parameters.Add("@ShipIDDropDownList", System.Data.SqlDbType.Int);
20 comm.Parameters["@ShipIDDropDownList"].Value = Convert.ToInt32(ShipIDDropDownList.SelectedValue);
21
22 conn.Open();
23 reader = comm.ExecuteReader();
24 if (reader.Read())
25 {
26 orderIDLbl.Text = reader["OrderID"].ToString();
27 customerIDLbl.Text = reader["CustomerID"].ToString();
28 dateLbl.Text = reader["Date"].ToString();
29 numofitemsLbl.Text = reader["NumberofItems"].ToString();
30 descripofitemsLbl.Text = reader["DescriptionsofItems"].ToString();
31 safeLbl.Text = reader["SafeItems"].ToString();
32 destinationLbl.Text = reader["Destination"].ToString();
33 }
34 reader.Close();
35 conn.Close();
36 conn.Dispose();
37 }
38 </script>
39
40 <asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
41 <br />
42 <table style="position: static">
43 <tr>
44 <td style="width: 147px">
45 <strong>ShipID:</strong></td>
46 <td style="width: 100px">
47 <asp:DropDownList ID="ShipIDDropDownList" runat="server" DataSourceID="SqlDataSource1"
48 DataTextField="ShipID" DataValueField="ShipID" Style="position: static">
49 </asp:DropDownList>
50 <asp:Button ID="ShipIDSelect" runat="server" Style="position: static" Text="Select" OnClick="ShipIDSelect_Click" />
51 <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ShippingSystemConnectionString1 %>"
52 SelectCommand="SELECT [ShipID] FROM [OrdersonShip]"></asp:SqlDataSource>
53 </td>
54 <td style="width: 100px">
55 </td>
56 </tr>
57 <tr>
58 <td style="width: 147px">
59 </td>
60 <td style="width: 100px">
61 </td>
62 <td style="width: 100px">
63 </td>
64 </tr>
65 <tr>
66 <td style="width: 147px">
67 <strong>OrderID:</strong></td>
68 <td style="width: 100px">
69 <asp:Label ID="orderIDLbl" runat="server" Style="position: static" Text="" Width="178px"></asp:Label></td>
70 <td style="width: 100px">
71 </td>
72 </tr>
73 <tr>
74 <td style="width: 147px">
75 <strong>CustomerID:</strong></td>
76 <td style="width: 100px">
77 <asp:Label ID="customerIDLbl" runat="server" Style="position: static" Text="" Width="177px"></asp:Label></td>
78 <td style="width: 100px">
79 </td>
80 </tr>
81 <tr>
82 <td style="width: 147px; height: 21px">
83 <strong>Date:</strong></td>
84 <td style="width: 100px; height: 21px">
85 <asp:Label ID="dateLbl" runat="server" Style="position: static" Text="" Width="177px"></asp:Label></td>
86 <td style="width: 100px; height: 21px">
87 </td>
88 </tr>
89 <tr>
90 <td style="width: 147px; height: 21px">
91 <strong>Number of Items:</strong></td>
92 <td style="width: 100px; height: 21px">
93 <asp:Label ID="numofitemsLbl" runat="server" Style="position: static" Text="" Width="177px"></asp:Label></td>
94 <td style="width: 100px; height: 21px">
95 </td>
96 </tr>
97 <tr>
98 <td style="width: 147px">
99 <strong>Description of Items:</strong></td>
100 <td style="width: 100px">
101 <asp:Label ID="descripofitemsLbl" runat="server" Style="position: static" Text="" Width="178px"></asp:Label></td>
102 <td style="width: 100px">
103 </td>
104 </tr>
105 <tr>
106 <td style="width: 147px">
107 <strong>Are Items Safe?:</strong></td>
108 <td style="width: 100px">
109 <asp:Label ID="safeLbl" runat="server" Style="position: static" Text="" Width="177px"></asp:Label></td>
110 <td style="width: 100px">
111 </td>
112 </tr>
113 <tr>
114 <td style="width: 147px">
115 <strong>Destination:</strong></td>
116 <td style="width: 100px">
117 <asp:Label ID="destinationLbl" runat="server" Style="position: static" Text="" Width="177px"></asp:Label></td>
118 <td style="width: 100px">
119 </td>
120 </tr>
121 </table>
122 </asp:Content> I get a Ambiguous column name 'OrderID'. Error. How do I fix it?The stack trace is below: [SqlException (0x80131904): Ambiguous column name 'OrderID'.]
System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) +98
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) +82
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) +346
System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) +3430
System.Data.SqlClient.SqlDataReader.ConsumeMetaData() +52
System.Data.SqlClient.SqlDataReader.get_MetaData() +130
System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) +371
System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) +1272
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) +334
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) +45
System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) +162
System.Data.SqlClient.SqlCommand.ExecuteReader() +114
ASP.ships_viewordersonship_aspx.ShipIDSelect_Click(Object sender, EventArgs e) in c:SystemShipsViewOrdersonShip.aspx:23
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +96
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +116
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +31
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +32
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +72
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3824
  Regards, Peter