"Plugin died unexpectedly" error message when browsing the Exchange Plugin. (4045796)

After a NetVault Client was upgraded from version 8.5.0 to 8.6.1, the following error message appeared when browsing the Exchange 4.5.6 Plugin on a standalone Exchange 2007 Client:

"A plugin died unexpectedly"

We made sure that we could ping, forward/reverse nslookup and telnet from the NetVault Server to Client and vice-versa and all was successful (except for forward/reverse nslookup from the NetVault Server as a Linux machine, but made sure that the Client IP Address and FQDN was entered in the hosts file, as was missing); as NetVault needs to communicate/resolve from the NetVault Server to the Client and vice-versa.
We then made sure that the User used for the Exchange Plugin has the following items, as per the pre-requisites of the Exchange Plugin User Guide:

- Be a valid domain or local account.
- Be a member of the Power Users group.
- Be a member of the domain’s Backup Operators group (for domain accounts).
- Be a member of the Backup Operators group on the machine that Exchange is running on.
- As well as Administrator

Made sure that the NetVault Client Process Manager – Logon tab now has the Domain Administrator login details instead of local administrator.
Also made sure that the Windows Firewall was disabled and was already disabled as part of a Group Policy.
Re-installed the Exchange License key (just in case this was corrupted) and still we were receiving the error message when browsing the Exchange Plugin.

We removed the Exchange Plugin from the NetVault Client, restarted the NetVault Server Services, installed the Exchange 4.6 Plugin instead and configured the Exchange Plugin.
Now we can browse the Exchange Plugin successfully.
So the problem could have been caused by the NetVault Client upgrade?