See forum post:
http://forum.pmease.com/viewtopic.php?f=1&t=2914

The stack trace is:

2013-12-20 02:27:25,369 [pool-1-thread-78946] ERROR org.hibernate.util.JDBCExceptionReporter - Duplicate entry '1387502845311-pc-509943-vm1:8811-disk.usage./' for key 'QB_TIMESTAMP'
2013-12-20 02:27:25,370 [pool-1-thread-78946] ERROR org.hibernate.event.def.AbstractFlushingEventListener - Could not synchronize database state with session
org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:275)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:268)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:184)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)
at com.pmease.quickbuild.entitymanager.impl.DefaultMeasurementDataManager.flushAndClear(DefaultMeasurementDataManager.java:71)
at com.pmease.quickbuild.entitymanager.impl.DefaultMeasurementDataManager.save(DefaultMeasurementDataManager.java:98)
at com.pmease.quickbuild.plugin.measurement.core.reporter.MeasurementServerReporter.save(MeasurementServerReporter.java:105)
at com.pmease.quickbuild.plugin.measurement.core.reporter.MeasurementServerReporter.access$100(MeasurementServerReporter.java:34)
at com.pmease.quickbuild.plugin.measurement.core.reporter.MeasurementServerReporter$NodeMetricsSender.execute(MeasurementServerReporter.java:93)
at com.pmease.quickbuild.grid.NodeJobExecuteJob.execute(NodeJobExecuteJob.java:26)
at com.pmease.quickbuild.grid.GridJob.run(GridJob.java:71)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.sql.BatchUpdateException: Duplicate entry '1387502845311-pc-509943-vm1:8811-disk.usage./' for key 'QB_TIMESTAMP'
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:2056)
at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:1467)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeBatch(NewProxyPreparedStatement.java:1723)
at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:70)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:268)
... 18 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '1387502845311-pc-509943-vm1:8811-disk.usage./' for key 'QB_TIMESTAMP'
at sun.reflect.GeneratedConstructorAccessor162.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4190)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4122)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2570)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2731)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2818)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2157)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2460)
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:2008)
... 22 more