Make sure there are no spaces in your install path. I ran into similar problem, when i moved the jboss home from 'program files' it corrected the problem
This might be as trivial as having jre in your %JAVA_HOME% variable as opposed to jdk.
jre does not have all the components needed for jboss to run. double check that you are pointing to JDK
your post suggests that you are pointing to jre.
an ejb is deployed after it's compiled so it will work with a jre.
plus if you read carefuly the error message it basically says that JBoss tried to access javac and didn't find it (hence NULL) javac is not included with jre.