If Disabling the AV doesn't fix this issue, then have their IT do a full uninstall/reinstall of MS Office before proceeding to the next steps. Uninstalling and then reinstalling Office was the only thing that worked in the example linked ticket, and having done that as a first or second step would have saved significant time.
I've repeatedly seen an issue with older versions of Eclipse where users will go to email using Outlook but there is no response from Outlook. Jon Valcik gave me the following fix:
1. Find the registry key here:
2. Under this key is a version number - in this case 9.6
3. Delete the 9.6 key and everything underneath it
4. Repaired office via Programs and Features (quick repair)
->This reregistered the Microsoft Outlook 16.0 Object Library and fixed the corrupt registry key.
Tested again using "Open in Outlook" in eclipse
Ticket example: https://help.piftech.com/a/tickets/46287