You are using all the connections available in the pool and JBoss cannot provide you with any unused connections when you request them. JBoss will eventually free connections when the connection idle timeout occurs and they are reaped and returned to the pool. However, it is generally the responsibility of the developer to build their systems so that connections are explicitly returned as soon as the component has finished doing work with the connection. Holding a connection for a long period is generally not good design practice and can lead to scalability problems.
I can only suggest reviewing your design and determine a better way to share this scarce resource. YMMV.