I have JBoss-4.2.2 GA with:
19:23:11,113 INFO [ServerInfo] Java version: 1.5.0_10,Sun Microsystems Inc. 19:23:11,113 INFO [ServerInfo] Java VM: Java HotSpot(TM) Server VM 1.5.0_10-b03,Sun Microsystems Inc. 19:23:11,113 INFO [ServerInfo] OS-System: Windows 2003 5.2,x86
I just tried hot deploying an ejb jar in the deploy folder, by deleting it and copying it back again. It worked. I even tried it with exploded deployment. Even that worked.
What is your operating system and also what's the version of Java?
I also made a test by manually (copy on file level) deploying the ejb.jar and redeploying it after having it changed slightly. this worked fine.
It seems that the error occurs when deploying it directly with help of the eclipse web tools platform.