It looks like you have another instance of MinaTaskServer running and you might want to shutdown the other one.
org.jbpm.task.service.mina.MinaTaskServer using port 9123
at org.jbpm.task.service.mina.BaseMinaTaskServer.run(BaseMinaTaskServer.java:53)
at java.lang.Thread.run(Unknown Source)
Caused by: java.net.BindException: Address already in use: bind
at sun.nio.ch.Net.bind(Native Method)