SUS update MailSite Express reports: Session required error After updating a server running MailSite Express with the Microsoft SUS update, MailSite Express stops functioning Microsoft states that you should only install SUS update on a dedicated machine OR one that doesn't not run any other critical IIS services. However, there is no documentation to that effect anywhere.

Installing SUS makes several changes to IIS not the least of which is to disable "Starting Sessions" in all the IIS virtual folder properties. This is in fact what causes the problem.

To correct this problem, go to the properties tab and re-enable "Allow Start Sessions".