Could you please describe better the circumstances, specifically:
1. are you sure that the archive is deployed? could you run it from your web browser or see it in the deploy directory?
2. aren't there some exceptions or other messages in the message log, server log, output console?
The output console should show the URL of the deployed archive, is that correct URL, i.e. the same URL you would use when trying to access the application maunally from the browser?
3. do you have the proxy in the NetBeans set correctly, especially aren't you accessing 'localhost' through the proxy? (check the Tools->Options dialog - search for the "No Proxy For" label in the General category)
3. what type of installation of JBoss server you have? (EJB3 or from the archive), did you make some post-installation changes into its configuration?
If the 'checklist' doesn't help you, please file the bug into the NetBeans Issuezilla, http://web.netbeans.org/issues/enter_bug.cgi?component=serverplugins, subcomponent jboss4. Please describe your project (type, how it was created), environment (JBoss version, installation, NB version, JDK version) and attach the logs I mentioned above. Your report will be very valuable in the case of such serious bug. Thank you.