Addendum: I have tested several permutations of the instructions here:
and they did not resolve the issue. So, repository=yes, core=asm or core=javassist, asm.jar (and/or javassist.jar) in $JBOSS_HOME/bin, no warnings in the log files.
I'm not even seeing the class entries like the previous poster.
The "core" option isn't supported anymore - and the jboss-profiler.jar file should be in the bin/ directory -- see the Installation chapter in the user guide.
If that doesn't work post the stacktrace and your run.conf and jboss-profiler.properties files.