Why can't the client receive the message from the server in UDP programing by applet?

I have meet a problem following that recentainly:  
  Why can't the client receive the message from the server in UDP programing When I use applet and frame?
  There are the following error in java control:
/************************************************/
com.ms.security.SecurityExceptionEx[JIMMessage.feedback]: cannot access 8000
   at com/ms/security/permissions/NetIOPermission.check
   at com/ms/security/PolicyEngine.deepCheck
   at com/ms/security/PolicyEngine.checkPermission
   at com/ms/security/StandardSecurityManager.chk
   at com/ms/security/StandardSecurityManager.checkListen
   at java/net/DatagramSocket.create
   at java/net/DatagramSocket.<init>
   at java/net/DatagramSocket.<init>
   at JIMMessage.feedback
   at JIMEnter.actionPerformed
   at java/awt/Button.processActionEvent
   at java/awt/Button.processEvent
   at java/awt/Component.dispatchEventImpl
   at java/awt/Component.dispatchEvent
   at java/awt/EventDispatchThread.run
com.ms.security.SecurityExceptionEx[JIMMessage.feedback]: cannot access 8000
     at java/net/DatagramSocket.CheckCanReceive
     at java/net/DatagramSocket.receive
     at JIMMessage.feedback
     at JIMEnter.actionPerformed
     at java/awt/Button.processActionEvent
     at java/awt/Button.processEvent
     at java/awt/Component.dispatchEventImpl
     at java/awt/Component.dispatchEvent
     at java/awt/EventDispatchThread.run
Exception occurred during event dispatching:
com.ms.security.SecurityExceptionEx[JIMMessage.feedback]: cannot access 8000
     at java/net/DatagramSocket.CheckCanReceive
     at java/net/DatagramSocket.receive
     at JIMMessage.feedback
     at JIMEnter.actionPerformed
     at java/awt/Button.processActionEvent
     at java/awt/Button.processEvent
     at java/awt/Component.dispatchEventImpl
     at java/awt/Component.dispatchEvent
     at java/awt/EventDispatchThread.run
/************************************************/
Thank you!
coffeeteaAsked:
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objectsConnect With a Mentor Commented:
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objectsCommented:
Is the machine your trying to connect to the same as the web server that the applet was loaded from?
Unsigned applet can only connect to the server that they were loaded from.
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jorjCommented:
Yes, that's it. You should sign your applet in order to connect to any other host than the one it was loaded from, including localhost  otherwise you will get a security exception.
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coffeeteaAuthor Commented:
 But how can I sign my applet?Can I sign my applet by writing security certificate code or applying for certificate on the certificate website?and that I can send the message but can't receive the message,why?
  Now I can receive the message through the attributes of Internet Explorer,but it isn't good solutions for the applet communication problem

   
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objectsCommented:
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coffeeteaAuthor Commented:
I have sit through the document,It is for the microsoft SDK for java. I haven't resolved the problem with the method which the document refer to now ,but I have got much Apocalypse,moreover,I'll try my best to resolve the problem with the above method .
   If  I work out,I'll send my points to you! Thank you very much!
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jorjCommented:
Maybe I can give you another ideea: you can do a redirecter programm which will run on the host and its only job is to act as a pipe between the applet and the target site. In this way you will not have to pay money for a certificate, and will work on all browsers.
Signing applets using other keys than the ones given by certain key providers will display a warning on the client's computer, and you may not want this.
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coffeeteaAuthor Commented:
:objects
    Thanks for your help,I'll read the documents and have a try!

:jorj
   Now the client can send message to the server,but the client can't receive the message from the sever.I think Internet Explorer intercept the message and forbid communicating with applet!What about your idea?Can you give me more details?
   Thank you!
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jorjCommented:
You cannot set a TCP server from the applet, because of the security manager, as we discussed already. Anyway, I use TCP to open a connection from the applet, then I obtain the connection's input and output streams and from here you can do whatever you want.

Be more specific: what have you done and what results have you obtained until now, regarding the applet side.
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coffeeteaAuthor Commented:
OK!
:jorj
  Thanks for helping me!

: objects  
  I fell for your solutions so I will accept your comment as an answer... your method is good!And I worked out with the documents which you offered.Thanks!

  Thanks everyone for helping me out!You are realy nice all of you!

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objectsCommented:
Thanks for the points :)
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