There could be two reasons for above problem.
1. You might have deployed same bean with different names. so i suggest you to clean deploy folder and redeploy them again. this generally happens if you use Manual deployment in eclipse/any IDE in general (export option).
2. Sometimes if forcefully shutdown jboss in its temp folder it will not delete the previous JNDI bindings. so stop jboss using stop.jar/bat
thanks for your suggestion Vikky but I am not using any IDE, as i told I am migrating the app from JBoss4 to JBoss5. Initially I though just deploying the ejb jar file will work but it didnt. I am facing new issues daily.
Double-check the contents of your EAR file. The new 5.0 deployers examine the contents of the application and launch new deployers based on those contents. This has caused issues with deploying certain app that have duplicated hteir contents (with the ill-formed MS SQL JDBC JAR file being one of them ore obvious examples).
By the way, did you notice that you didn't post the logs? Also, post the contents of your ear, using: jar -tf xxx.ear