about "error establishing socket"??

hi,experts,in my project ,about some time (10s or 30s) ,the error" java.sql.SqLException:[Microsoft] [SQLServer:2000 driver for jdbc] Error establishing socket" will show in tomcat console.i use sqlserver2000 + sp3 + win2000 server,and my code like this:

<%@ page contentType="text/html; charset=gb2312" %>
<% request.setCharacterEncoding("gb2312"); %>
<%@ page import="java.sql.*"%>
<%
            String sqlDriver = "com.microsoft.jdbc.sqlserver.SQLServerDriver";
            String sqlJdbc = "jdbc:microsoft:sqlserver://btns:1433;DatabaseName=CommunityMedical";
            String sqlUser = "sa";
            String sqlPwd = "btn";
            try {
                  Class.forName(sqlDriver);
                  Connection conn = DriverManager.getConnection(sqlJdbc, sqlUser, sqlPwd);
                  java.sql.Statement stmt = conn.createStatement();
            java.sql.ResultSet rs=stmt.executeQuery("select 1");
            if(rs.next()){
              out.println("ok");
            }
            } catch (Exception e) {
                  out.println(e);
            }
%>

why the error is show????

thanks!