JBoss 6.x is built against slf4j 1.5.6 and modeshape since about 2.6 has been using slf4j 1.6.1. The slf4j API checks the version when it binds with the logging backend (in slf4j-jboss-logmanager.jar for jboss 6) and complains if it finds a major version number difference (such as 1.6 to 1.5). Major version changes can include API differences hence the warning.
It should still work OK as it is just a warning, I have systems in production that print this warning at startup (caused by a difficult version mismatch between slf4j, log4j and logback).
Unfortunately there seems to be an API difference that is causing the runtime to fail. I have looked around and this seems a common issue with no straightforward solution (e.g. https://community.jboss.org/message/567177).
I have also tried to run modeshape in JBoss 7 but I ran into some other issue that I can't remember.
Starting repositories ...
Shutting down repositories ... SLF4J: slf4j-api 1.6.x (or later) is incompatible with this binding.
SLF4J: Your binding is version 1.5.5 or earlier.
SLF4J: Upgrade your binding to version 1.6.x. or 2.0.x
Exception in thread "Thread-1" java.lang.NoSuchMethodError: org.slf4j.impl.StaticLoggerBinder.getSingleton()Lorg/slf4j/impl/StaticLoggerBinder;
BTW, my only dependency on JBoss to run that example comes from the Jaas config that uses the org.jboss.security.auth.spi.UsersRolesLoginModule login module.
I have searched around trying to disable that, I am just trying to explore modeshape features at this point, but I couldn't find an easy way to do so... I would be happy with just anonymous, unauthenticated access at this point...