Thanks Gertjan.
First I've tried adding permissions to the temporary ASP.NET Files like you mentioned, it already had Modify access via IIS-USR which I increased to Full. I stopped the Index service and performed an IISReset /restart.
I then accessed AE via IE11 and unlike yesterday when I opened my inbox in the archive, I can see archived items. So that is an improvement. I can search for a specific user and it looks like the search component is now working.
Trouble now is when I try to click on an item to view it, a new tab opens and I get
"Symantec Enterprise Vault - Error
The Enterprise Vault service is not available. "
I've tried the following
https://www.veritas.com/support/en_US/article.100009900
Ran the poweshell script to check for blocked files. Nothing found.
used aspnet_regiis -iru to re-register into IIS.. no joy.
https://www.veritas.com/support/en_US/article.100011786
Removing HTTP Activation and Non-HTTP Activation from .Net3.5 and adding back again - no joy
https://www.veritas.com/support/en_US/article.100030535
All those scenarios checked and look fine - I've reapplied the permissions on the Webapp folder too - no change
Also I ran DS to see what that found and the only thing suggested was a minor issue pointing to this KB
https://support.microsoft.com/en-gb/help/2803161/net-tcp-does-not-have-an-implementation-of-hostedtransportconfiguratio
Looking at our %windir%\Microsoft.NET\Framework64\v2.0.50727\CONFIG\web.config method 1 in the KB article doesn't exist in there. Not changed it yet as the items in my archive can be seen but I cannot open them now.
Still getting the exact same DCOM errors in the event logs but the W3WP Dtrace looks better initially than yesterdays before it hits the DCOM error...
9 12:15:11.539 [5688] (w3wp) <6644> EV-L {Slot.Page_Load} Slot.Page_Load
10 12:15:11.539 [5688] (w3wp) <6644> EV-L {Slot.GetSyncSlot} Slot.GetSyncSlot - VEID:1D50062C880FD5E4594D5C1FD912DDD2F1110000evault2, TimeOut:0
11 12:15:11.539 [5688] (w3wp) <6644> EV:L {CAutoJournalAccessor::GetSyncSlot} (Entry)
13 12:15:11.550 [5688] (w3wp) <6644> EV:L CBaseDirectoryServiceWrapper::CreateDirectoryService() - Entry [m_nNumTries = 40]
14 12:15:11.552 [5688] (w3wp) <6644> EV:L CBaseDirectoryServiceWrapper::CreateDirectoryService() - Successfully communicated with an EV Directory Service on the local machine
17 12:15:11.583 [5688] (w3wp) <6644> EV:L {VaultCoCreateInstanceEx} CLSID [{4EC6FF76-C97A-11D1-90E0-0000F879BE6A}] Server Name [(null)] Used Server Name [(null)] Num of attempts [1] Total elapsed [0.000s] Result [Success (0)]
18 12:15:11.584 [5688] (w3wp) <6644> EV:L {GetStorageObject:#46} Calling VaultCoCreateInstanceEx
19 12:15:11.584 [5688] (w3wp) <6644> EV:L {CStorageOnlineOpnsInstanceHelper::GetLoadBalancedStorageOnlineOpnsCLSID:#61} Non-StorageOnlineOpns CLSID. Returning Input.
20 12:15:11.694 [5688] (w3wp) <6644> EV:L {VaultCoCreateInstanceEx} Attempt [1] to create COM object failed. CLSID [{957FF4B4-162B-4708-843A-0134868699B4}] Server Name [hostnamet] Elapsed [0.110s] Result [Access is denied. (0x80070005)]
21 12:15:11.899 [5688] (w3wp) <6644> EV:L CHostNameHelper: IsLocalMachineExtendedCheck returned [True] for server [hostname].
This component - {957FF4B4-162B-4708-843A-0134868699B4} seems to be the StorageOnlineOpns.JournalAccessor looking through the Registry but cannot find any similar issues on the Support portal.
Your final idea of re-installing the binaries scares the hell out of me. Not sure I would know where to start with that..just install 11.0.1 over the top then upgrade to CHF5 or just run the upgrade again? I've got a funny feeling some of these servers might have been upgraded from V10 to 11 by our previous Evault person before he left.