FC can throw a ConcurrentModificationException on a view change.

The following code is not correct:

for(Address creditor: creditors) {
if(!mbrs.contains(creditor))
creditors.remove(creditor);
}

To fix it replace it with something like that:
for(Iterator<Address> it=creditors.iterator(); it.hasNext() {
Address creditor = (Address)it.next();
if(!mbrs.contains(creditor))
it.remove();
}

Here is the exception:
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:841)
at java.util.HashMap$KeyIterator.next(HashMap.java:877)
at org.jgroups.protocols.FC.handleViewChange(FC.java:791)
at org.jgroups.protocols.FC.up(FC.java:422)
at org.jgroups.protocols.pbcast.GMS.installView(GMS.java:500)
at org.jgroups.protocols.pbcast.CoordGmsImpl.handleViewChange(CoordGmsImpl.java:430)
at org.jgroups.protocols.pbcast.GMS.up(GMS.java:663)
at org.jgroups.protocols.VIEW_SYNC.up(VIEW_SYNC.java:193)
at org.jgroups.protocols.pbcast.STABLE.up(STABLE.java:234)
at org.jgroups.protocols.UNICAST.up(UNICAST.java:293)
at org.jgroups.protocols.pbcast.NAKACK.handleMessage(NAKACK.java:858)
at org.jgroups.protocols.pbcast.NAKACK.up(NAKACK.java:687)
at org.jgroups.protocols.BARRIER.up(BARRIER.java:136)
at org.jgroups.protocols.VERIFY_SUSPECT.up(VERIFY_SUSPECT.java:167)
at org.jgroups.protocols.FD.up(FD.java:285)
at org.jgroups.protocols.FD_SOCK.up(FD_SOCK.java:308)
at org.jgroups.protocols.MERGE2.up(MERGE2.java:145)
at org.jgroups.protocols.Discovery.up(Discovery.java:245)
at org.jgroups.protocols.TP.passMessageUp(TP.java:1132)
at org.jgroups.protocols.TP.access$100(TP.java:48)
at org.jgroups.protocols.TP$1.run(TP.java:1035)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
at java.lang.Thread.run(Thread.java:595)