I\'m a newbie with maven, spring, embedded glassfish, dependency conflicts ( I don\'t know how to see them and how to solve them)... and I can\'t fix this problem alone even
Try to downgrade SLF4J version. This error usually pops up when some library requires older / newer version of SLF4J.
Also make sure that if you have more than one SLF4J JAR file in classpath that they all are from the same SLF4J version (right now it seems that this is not your problem).
EDIT: I overlooked that it is embedded glassfish-only problem. I don't use Glassfish, but the problem will be with mixing different versions of SLF4J. See which SLF4J version Glassfish uses and use the same.