HTTP Error 500

We met http error 500 for certain transmissions when GTM sends Trade Transaction Line back to EBS. Error disappeared upon re-processing.
Understanding it is a generic "catch-all" error and we can explore to set a few re-attempt times, I am trying to understand from experts usually in what situation can this happen. This does Not happen very often here. Just once in a few days.

Error Details are as below and thanks in advance!
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2014-05-01 16:40:00.767 Error Exception HTTP Failure on http://<GTMServer>/webservices/TransportAgentServer: 500

at sun.reflect.GeneratedConstructorAccessor2019.newIn stance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newI nstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Construc tor.java:513)
at glog.util.exception.GLException.factory(GLExceptio n.java:435)
at glog.util.exception.GLException.factory(GLExceptio n.java:411)
at glog.util.exception.GLException.factory(GLExceptio n.java:407)
at glog.util.exception.GLException.factory(GLExceptio n.java:403)
at glog.util.httppost.HttpPostEvent$Listener.doPost(H ttpPostEvent.java:383)
at glog.util.httppost.HttpPostEvent$Listener.trigger( HttpPostEvent.java:241)
at glog.util.event.MemoryEventQueueRunnable.processEv ent(MemoryEventQueueRunnable.java:146)
at glog.util.event.MemoryEventQueueRunnable.run(Memor yEventQueueRunnable.java:98)
at glog.util.event.EventThread.run(EventThread.java:8 6)
at java.lang.Thread.run(Thread.java:619)
[transport - HTTP - 1]