I do also get the same error from time to time when starting a test. The test stops and when I start next time it works. I never get the error two times in a row. This is from the neoload.log :

2015/04/14 13:05:02 ERROR - neoload.Agents: Failed to start and register Load Generator: Load Generator off: process created but not registered after waiting delay (key "lg.start.delay" in agent.properties).
2015/04/14 13:05:02 WARN - neoload.Runtime: Can't start the Load Generator localhost com.neotys.nl.controller.hb: Failed to start Load Generator on localhost. The Load Generator process has been created but has not registered after waiting delay (key "lg.start.delay" in agent.properties). : an error occured while communicating with 'localhost'
at com.neotys.nl.controller.tb.a(tb.java:419)
at com.neotys.nl.controller.tc.a(tc.java:367)
at com.neotys.nl.controller.p.d.d.a(d.java:371)
at com.neotys.nl.controller.p.d.d.a(d.java:137)
at com.neotys.nl.controller.p.d.c.call(c.java:118)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

2015/04/14 13:05:02 ERROR - neoload.Gui: Unable to start Load Generator localhost com.neotys.nl.controller.hb: Failed to start Load Generator on localhost. The Load Generator process has been created but has not registered after waiting delay (key "lg.start.delay" in agent.properties). : an error occured while communicating with 'localhost'
at com.neotys.nl.controller.tb.a(tb.java:419)
at com.neotys.nl.controller.tc.a(tc.java:367)
at com.neotys.nl.controller.p.d.d.a(d.java:371)
at com.neotys.nl.controller.p.d.d.a(d.java:137)
at com.neotys.nl.controller.p.d.c.call(c.java:118)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

2015/04/14 13:05:53 WARN - neoload.Runtime: No Load Generator available to play the scenario. Scenario stopped.
2015/04/14 13:05:53 ERROR - neoload.Gui: No Load Generator available to play the scenario. Scenario stopped.
2015/04/14 13:06:46 INFO - neoload.Configuration: The project Nya_Webb_och_Expert_2015_PUID was successfully loaded in 3.429 sec.
2015/04/14 13:06:53 WARN - neoload.Network: [TunneledSocket-127.0.0.1:59485-to-127.0.0.1:59487]Tunnel data transfert error java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:196)
at java.net.SocketInputStream.read(SocketInputStream.java:122)
at java.net.SocketInputStream.read(SocketInputStream.java:108)
at com.neotys.l.f.t.run(t.java:30)

2015/04/14 13:06:53 WARN - neoload.Network: [TunneledSocket-127.0.0.1:59487-to-127.0.0.1:59485]Tunnel data transfert error java.net.SocketException: socket closed
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:152)
at java.net.SocketInputStream.read(SocketInputStream.java:122)
at java.net.SocketInputStream.read(SocketInputStream.java:108)
at com.neotys.l.f.t.run(t.java:30)