Trying to stop any 'Upgrade', 'Synchronize' and 'Rebuild' tasks returns the error:
"The subtask for '

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[[Symantec.EnterpriseVault.Indexing.Common.CommunicationFault, EVSharedManagedInterfaces, Version=10.0.3.0, Culture=neutral, PublicKeyToken=26c5e2ccf2b9267c]]
Reference: An error occurred while invoking Void
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.