In place Windows 10 Upgrade - Task Sequence Manager could not initialize Task Sequence Environment. code 80070005

[SighBee 0]

I've set up a task sequence to run an in-place upgrade to Windows 10 and it's run successfully on nearly 100 machines. One machine has just encountered an error I can't decipher. According to smsts.log, it completed the first part of the upgrade on Friday evening (today is the following Monday) and then rebooted but the next entry isn't until this morning, which is strange. I'm not sure if the machine crashed but it appears not. When the user logged on this morning, Windows 10 was in a funny state with no start button and no network connectivity. Rebooting the laptop initiated a rollback and the PC is back working correctly on Windows 7.

When the log continues, there appears to be an "access denied" error when trying to load the TS environment:

Quote

Opening Task Sequencing Environment    TSManager    10/04/2017 08:37:02    6232 (0x1858)
hMap != 0, HRESULT=80070005 (e:\nts_sccm_release\sms\framework\tscore\environmentscope.cpp,493)    TSManager    10/04/2017 08:37:02    6232 (0x1858)
m_pGlobalScope->open(), HRESULT=80070005 (e:\nts_sccm_release\sms\framework\tscore\environmentlib.cpp,335)    TSManager    10/04/2017 08:37:02    6232 (0x1858)
Environment::SharedEnvironment.open(), HRESULT=80070005 (e:\nts_sccm_release\sms\client\tasksequence\tsmanager\tsmanager.cpp,1439)    TSManager    10/04/2017 08:37:02    6232 (0x1858)
Failed to open environment. code 80070005    TSManager    10/04/2017 08:37:02    6232 (0x1858)
Task Sequence Manager could not initialize Task Sequence Environment. code 80070005    TSManager    10/04/2017 08:37:02    6232 (0x1858)
hr = InitializeEnvironment(), HRESULT=80070005 (e:\nts_sccm_release\sms\client\tasksequence\tsmanager\tsmanager.cpp,1213)    TSManager    10/04/2017 08:37:02    6232 (0x1858)
Task sequence execution failed with error code 80070005    TSManager    10/04/2017 08:37:02    6232 (0x1858)
Cleaning Up.    TSManager    10/04/2017 08:37:02    6232 (0x1858)

Can anybody explain what is generating the error and how I can fix it? Thanks!