Hi,
I will fix this in the next release of Event Calendar Pro so that it works for content admins. I will also make it configurable if you want to allow anyone with edit permission to delete orders, you'll be able to add this in user.config:
<add key="EventCalendarPro:AllowNonAdminEditorsToDeleteOrders" value="true" />
However I don't have a target date at the moment for the next update.
Hope that helps,
Joe