"The messaging interface has returned an unknown error"

Hi

EV version is 8.0.3, client Outlook version across the estate is Outlook XP/2002. The user gets the error in the title. We have carried out a complete removal of the EV client from the users machine and reinstalled after a restart. This has not changed the issue.

We have also confirmed that the email, when removed from the vault, opens without any issue.

 

Any ideas?

 

Many thanks