When saving an event with a reminder in your Outlook calendar, you may get this warning:
The reminder for “xxxx” will not appear because the item is in a folder that doesn’t support reminders. Is this OK?
This is because the calendar you’ve saved the event to is in a PST folder that doesn’t support reminders.
To fix this, in the list of calendars under “My Calendars” (on the left hand side of the Calendar panel), see what the name is of the folder that contains the calendar is. Then go back to your main email view and scroll through the panel on the left to find the top level folder (aka the PST file) with the same name. Right click the folder and click “Data File Properties”. Check the “Display reminders and tasks from this folder in the To-Do bar” then click “OK”.