The following error started occurring after trying to run a DS (Deployment Solution) Task:

Operation 'Start' failed for instance: 4a56f09b-d9ae-4611-92e0-3a529598513c
Could not load file or assembly 'Symantec.Deployment.TaskServerHandler, Version=8.1.0.0, Culture=neutral, PublicKeyToken=d3604070d7fd3e08' or one of its dependencies. The system cannot find the file specified.

Operation 'Start' failed for instance: 4a56f09b-d9ae-4611-92e0-3a529598513c
Could not load file or assembly 'Symantec.Deployment.TaskServerHandler, Version=8.1.0.0, Culture=neutral, PublicKeyToken=d3604070d7fd3e08' or one of its dependencies. The system cannot find the file specified.
   [System.IO.FileNotFoundException @ mscorlib]
   at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection)
   at System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection)
   at System.Reflection.Assembly.Load(String assemblyString)
   at Altiris.DotNetLib.Reflection.ObjectCreator.Create(String objType, String objAssembly)
   at Altiris.ClientTask.Server.Execution.ClientTaskExecutionEngine.GetTaskHandler(IBaseTaskExecutionInstance instance)
   at Altiris.TaskManagement.Common.Execution.Engine.TaskExecutionEngine.ProcessTaskExecuteOperation(TaskInstanceRequest request)

Exception logged from:
   at Altiris.DotNetLib.Logging.AtrsLog.ExceptionMessage(String message, Exception exception)
   at Altiris.TaskManagement.Common.Execution.Engine.TaskExecutionEngine.OnRequestException(Exception e, TaskInstanceRequest request)
   at Altiris.ClientTask.Server.Execution.ClientTaskExecutionEngine.OnRequestException(Exception e, TaskInstanceRequest request)
   at Altiris.TaskManagement.Common.Execution.Engine.TaskExecutionEngine.ProcessTaskExecuteOperation(TaskInstanceRequest request)
   at Altiris.TaskManagement.Common.Execution.Engine.TaskExecutionEngine.ProcessTaskInstanceRequest(TaskInstanceRequest request)
   at Altiris.ClientTask.Server.Execution.ClientTaskExecutionEngine.ProcessTaskInstanceRequest(TaskInstanceRequest request)
   at Altiris.TaskManagement.Common.Execution.Engine.TaskExecutionEngine.ProcessWorkToDoObject(Object nextWork)
   at Altiris.DotNetLib.Threading.AtrsThreadPoolEx.ProcessWorkToDo(Thread me, AtrsThreadPoolWorkItemEx work)
   at Altiris.DotNetLib.Threading.AtrsThreadPoolEx.ProcessWorkToDo()
   at Altiris.DotNetLib.Threading.AtrsThreadPoolEx.WorkerThreadRun()
   at Altiris.DotNetLib.Threading.AtrsThreadPoolEx.WorkerThreadProc()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

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Date: 3/27/2019 1:14:24 PM, Tick Count: 79854758 (22:10:54.7580000), Size: 3.47 KB
Process: AtrsHost (8252), Thread ID: 76, Module: AtrsHost.exe
Priority: 2, Source: ClientTaskExecutionEngine
 

ITMS 8.1 RU7

All those issues are related to DS Task Server handler not being installed properly.

Try the following:

1. Find the TaskHandlerInstall_x64.bat file in "...\Program Files\Altiris\Notification Server\NSCap\bin\Win64\X64\Deployment\Task Server Handler" (or look for the x86 file under ...\win32\x86\... if it is not a x64 machine)
2. Run the batch file manually.
3. If the problem persists, try running from a command prompt (as Administrator) the following MSI located in the same location as the "TaskHandlerInstall_x64.bat" :
   msiexec.exe /i "Symantec_DeploymentSolutionTaskServerHandler_8_1_x64.msi" skipaim=1 REBOOT=ReallySuppress
4. If the issue still persists, try uninstalling it and installing again:
   --To uninistall
   msiexec.exe /x "Symantec_DeploymentSolutionTaskServerHandler_8_1_x64.msi" skipaim=1 REBOOT=ReallySuppress
   --To install (with msi logging in case you need to review why the MSI is failing)
   msiexec.exe /i "Symantec_DeploymentSolutionTaskServerHandler_8_1_x64.msi" skipaim=1 REBOOT=ReallySuppress /l*v "C:\TSHmsi.log