Trying to stop any 'Upgrade', 'Synchronize' and 'Rebuild' tasks returns the error:
"The subtask for '' could not be stopped: Reason: 0x8013150b"</user archive>

or

Generating the following error in the event viewer:
Event ID: 40966
Task Category: Index Admin Service
Level: Error
Description: A program fault has raised an exception.
Exception: Failed to get subtask for subtask ID 17D2DB9C8E05D49F6B71ECED6CBC3E98613b00ev1
Diagnostic:
Type: System.ServiceModel.FaultException`1[[EnterpriseVault.Indexing.Common.CommunicationFault, EVSharedManagedInterfaces, Version=10.0.3.0, Culture=neutral, PublicKeyToken=26c5e2ccf2b9267c]]
Reference: An error occurred while invoking Void b__f().
Error Context : Stopping sub task for TaskEntryId 12DD149F8BC2262478807BEF2FAE284741013a00ev1 and SubTaskEntryId 17D2DB9C8E05D49F6B71ECED6CBC3E9861013b00ev1
Command Line: "C:\Program Files(x86)\Enterprise Vault\EVIndexAdminService.exe" -EntryID:1410C9C6F53A8DE4D932D9087D28C4C841710000ev1
Application Domain: EVIndexAdminService.exe
Process Id: 2700
Thread Id: 5212
V-437-40966
DTRACE Information:
To validate if this is the issue a DTRACE is needed, please perform the following steps on the EV server that has generated Event ID 40966 while re-creating the issue.
(EVIndexQueryServer) <6140> EV-H {INDEXQUERYSERVERAPPLICATION.EN_US} Innermost exception from previous error: System.IO.FileLoadException: Retrieving the COM class factory for component with CLSID {BD7A3509-B3F3-42FC-8FFE-FE8D1CCFE013} failed due to the following error: 8007045a.| at BuildUp_KVS.EnterpriseVault.Interop.AuditWrapperClass(IBuilderContext )| at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context) at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)
The CLSID {BD7A3509-B3F3-42FC-8FFE-FE8D1CCFE013} corresponds to the C:\Program Files(x86)\Enterprise Vault\x64\AuditWrapper.dll; a manual AuditWrapper.dll re-registration ("regsvr32.exe C:\Program Files(x86)\Enterprise Vault\x64\AuditWrapper.dll") fails like:

The CLSID {BD7A3509-B3F3-42FC-8FFE-FE8D1CCFE013} cannot be properly initialized because the following path "HKEY_LOCAL_MACHINE\SOFTWARE\KVS\Enterprise Vault\FIPS" has not been created during the EV binaries installation
A working Enterprise Vault (FIPS compliant DOC4820) installation must have the FIPS registry key in the following paths:
HKEY_LOCAL_MACHINE\SOFTWARE\KVS\Enterprise Vault\FIPS
"InstallPath=C:\Program Files(x86)\Enterprise Vault\x64"
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\KVS\Enterprise Vault\FIPS
"InstallPath=C:\Program Files(x86)\Enterprise Vault\"
Workaround:
Manually create the missing registry path in order to facilitate the process using the text files attached at the bottom of this article.
Warning: Incorrect use of the Windows registry editor may prevent the operating system from functioning properly. Great care should be taken when making changes to a Windows registry. Registry modifications should only be carried-out by persons experienced in the use of the registry editor application. It is recommended that a complete backup of the registry and workstation be made prior to making any registry changes.
After the upgrade to Enterprise Vault 10.0.1 (or newer releases) it is not possible to properly execute indexing upgrade, synchronize and rebuild tasks, newly archived items are not indexed; the new tasks created stay in 'inactive' state even if the 'Index Administration Task' is scheduled to run.