I have a user that has ZCS NE at 5.0.15 and ZCO 5.0.2931.15. The other day, they received a meeting invite from an outside party to multiple attendees. After they accepted, they got a Server Failure Notice email. The error_report.xml is attached (with some content deleted).
I did not see anything about something like this in an initial scan through the Product Portal for 5.0.