Exchange Store Manager (ESM) MAPI error 80040111 after upgrading to Archive Manager 5.1.2. (4238436)

Exchange Store Manager (ESM) MAPI error 80040111 after upgrading to Archive Manager 5.1.2.

AM server : Windows server 2012 R2
AM version : 5.1.2
Exchange : 2013
SQL Server : 2012

After an upgrade of the archive manager (4.5 --> 4.8 --> 5.1.2), the following error occured:

16:31:34 ERROR: Session.OpenMsgStore:
16:31:34 MAPI error 80040111
16:31:34 Error: The information store could not be opened.
16:31:34 Component: MAPI 1.0
16:31:34 Context: 00000286
16:31:34 Statistics for this run
16:31:34 _____________________________________
16:31:34 Folders processed : 0
16:31:34 Messages processed : 0 (0 linked)
16:31:34 Attachments processed : 0
16:31:34 Errors : 1
16:31:34 Warnings : 0
16:31:34 Mailbox export complete.

The following items were implemented from this KBA (https://support.quest.com/archive-manager/kb/138049):

**Test Internal and External proxy addresses in OWA.
**There is a high probability the External works and the Internal fails due to the fact the Internal name is not on the issued certificate and Archive Manager is trying to connect via the internal address. If this error occurs after an upgrade, test by looking at wlogs prior to the upgrade to see if the ProxyServer matches the one in the logs after the upgrade.
**Workaround. The following item can be added to Configuration Console...

Item Name: Autodiscover Override Settings
Value: ProxyAuthScheme=NTLM;ProxyServer=mail.domain.com (ProxyServer item was added along with the internal Proxy address to correct the issue).

Note: Please make sure that the Proxy Server FQDN is correct, otherwise will result in a "MAPI error 80040111" as well.

Unfortunately this didn't resolve the issue.