Symantec Management Platform (Notification Server)

I've got a few weekly reboot tasks set up, and they've been working fine until this week. Now, they're all failing and I'm seeing this error when I look at the status of each machine in the results:

An unknown exception was thrown.

System.Net.WebException: The remote server returned an error: (401) Unauthorized. at System.Net.HttpWebRequest.GetResponse() at Altiris.ClientTask.Server.Communication.NotificationServerWebConnection.PostToNotificationServer(String url, ICredentials credentials, NSWebConnectionBuildRequestStreamDelegate requestStreamDelegate, Int32 nMaxAttempts, Int32 nTimeout) at Altiris.ClientTask.Server.Communication.NotificationServerWebConnection.PostToNotificationServerAndCheckResponse(String url, NSWebConnectionBuildRequestStreamDelegate requestStreamDelegate, Stream& responseStream, StreamReader& sr, XmlTextReader& r, Int32 nMaxAttempts, Int32 nTimeout) at Altiris.ClientTask.Server.Communication.NotificationServerWebConnection.GetClientNetworkInformation(AltirisResourceGuid resourceGuid) at Altiris.ClientTask.Server.RemoteClientTaskManager.GetNetworkInformationForClient(ClientStatus client) at Altiris.ClientTask.Server.RemoteClientTaskManager.SendWakeOnLan(AltirisResourceGuid resourceGuid, Int32 portNumber) at Altiris.ClientTask.Server.Tasks.ShutdownTaskHandler.ExecuteOnRemoteResource() at Altiris.ClientTask.Server.Tasks.BaseRemoteClientTaskHandler.OnExecute(AltirisResourceGuid assignedResource, ParameterValueCollection inputParameters) at Altiris.ClientTask.Server.Tasks.BaseClientTaskHandler.OnExecute(AltirisResourceGuid assignedResource, ITaskExecutionEngine engine, IBaseTaskExecutionInstance instance, TaskInstanceRequest request) at Altiris.ClientTask.Server.Tasks.BaseClientTaskHandler.Execute(ITaskExecutionEngine engine, IBaseTaskExecutionInstance instance, TaskInstanceRequest request) at Altiris.ClientTask.Server.Execution.ClientTaskEngineExecutionThread.ExecuteTaskHandler()

Can anyone make sense of this? I couldn't seem to find this particular error on any searches.

Did you specify a particular account to run the task, along with a password?  Did that user's account have a changed password, changed access, etc?  Was it disabled or did it have administrator access revoked?  This looks like a permissions issue.