Outlook 2013 disables the Reserve Outlook add-in during startup. You see a warning near the top of Outlook and on the Outlook Options page that says: “A problem was detected with an add-in and it has been disabled.” When you View Disabled Add-ins, Outlook will report: “This add-in caused Outlook to start slowly.”
Outlook 2013 has become more strict when checking add-in performance. Outlook enforces that all add-ins consistently load faster than 1000 milliseconds. On some machines, it may take slightly more than one second for the Reserve add-in to load. This can be due to many environmental factors, including disk speed. If it takes longer than the 1 second, Outlook will disable the add-in. The user will be informed of this and will have the option to enable the add-in again.
System administrators can configure Outlook to always enable the Reserve add-in. For information from Microsoft about how to override this behavior via Group Policy, see the following Microsoft link.