Users suddenly stopped receiving Human Task related email Notifications. When I checked the SessionInfo table no new entries are getting created in the table. Not sure what triggered this issue. I checked the logs and found the following error message in the logs. Can anyone suggest how I can resolve this issue?

2015-12-14 02:23:49,030 ERROR [org.jbpm.task.service.TaskService] (pool-27-thread-2) 2015-12-14 02:23:49,030 ERROR [org.jbpm.task.service.TaskService] (pool-27-thread-2) Operation failed

java.lang.RuntimeException: Operation failed

  at org.jbpm.task.service.TaskServiceSession.executeEscalatedDeadline(TaskServiceSession.java:1108)

  at org.jbpm.task.service.TaskService.executeEscalatedDeadline(TaskService.java:285)

  at org.jbpm.task.service.TaskService$ScheduledTaskDeadline.call(TaskService.java:421)

  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)

  at java.util.concurrent.FutureTask.run(FutureTask.java:138)

  at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98)

  at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:206)

  at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)

  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)

  at java.lang.Thread.run(Thread.java:662)

Caused by: [Error: null pointer or function not found: �]

[Line: 1, Column: 1]

  at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.getMethod(ReflectiveAccessorOptimizer.java:1022)

  at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.getMethod(ReflectiveAccessorOptimizer.java:987)

  at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.getBeanProperty(ReflectiveAccessorOptimizer.java:677)

  at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.getBeanPropertyAO(ReflectiveAccessorOptimizer.java:472)

  at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.compileGetChain(ReflectiveAccessorOptimizer.java:374)

  at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.optimizeAccessor(ReflectiveAccessorOptimizer.java:143)

  at org.mvel2.ast.ASTNode.optimize(ASTNode.java:159)

  at org.mvel2.ast.ASTNode.getReducedValueAccelerated(ASTNode.java:115)

  at org.mvel2.MVELRuntime.execute(MVELRuntime.java:85)

  at org.mvel2.compiler.CompiledExpression.getDirectValue(CompiledExpression.java:123)

  at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:119)

  at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:113)

  at org.mvel2.MVEL.executeExpression(MVEL.java:906)

  at org.jbpm.task.service.TaskService.eval(TaskService.java:392)

  at org.jbpm.task.service.TaskService.eval(TaskService.java:361)

  at org.jbpm.task.service.DefaultEscalatedDeadlineHandler.executeEmailNotification(DefaultEscalatedDeadlineHandler.java:203)

  at org.jbpm.task.service.DefaultEscalatedDeadlineHandler.executeEscalatedDeadline(DefaultEscalatedDeadlineHandler.java:158)

  at org.jbpm.task.service.TaskServiceSession.executeEscalatedDeadline(TaskServiceSession.java:1093)

  ... 9 more