When JBoss attempts to deploy the rar file, it was throwing this error:
ERROR [org.apache.activemq.ra.ActiveMQEndpointWorker] (MSC service thread 1-4) Work Manager did not
accept work: : javax.resource.spi.work.WorkException: IJ000257:
org.apache.activemq.ra.ActiveMQEndpointWorker$1: Run method is synchronized
One member on the forum modified the source code for org.apache.activemq.ra.ActiveMQEndpointWorker and took out the "synchronized" keyword from the "run" method (line 97), and this fixed the problem. I modified the code as well and it fixed my problem too. According to a JBoss representative, ActiveMQ is out of spec on this, and claims that this should be fixed on the ActiveMQ side.
Please consider modifying this class. Otherwise, nobody will be able to use the resource adapter with JBoss.