how to invoke a ejb form servlets

[shawfly]

I have deployed a ejb whose jndi name is ejb/Member.Aplication client can invoke the ejb using the following code.However,when I copy these codes to one of my servlet,I can only get a null home pointer.
Please help me.Thanks very much.
using jboss 3.2.1+tomcat 4.1.24.
code:
props = new Properties();
props.put("java.naming.factory.initial", "org.jnp.interfaces.NamingContextFactory");
props.put("java.naming.factory.url.pkgs", "org.jboss.naming:org.jnp.interfaces");
props.put("java.naming.provider.url", "localhost:1099");
try
{
ctx = new InitialContext(props);
MemberHome theMemberHome = (MemberHome) ctx.lookup("ejb/Member");
}
catch (Exception e)
{
e.printStackTrace();
}