Probably a classloading issue? Are you packaging any jar(s) which contains javax.transaction.* related classes, as part of your application? If yes, then see if removing that jar from your package solves the issue.
You're correct! I had to include the hibernate-search jar to override the versions that are present in JBoss's class loader. When I did the jta jar was included as a transitive dependency. I excluded it and it worked. Thanks for you help!