Please note, that OroCalendarBundle 2.6.2 is not compatible with OroCRM 2.6.1 or OroCommerce 2.6.1
If you are not using our default applications (crm-application or orocommerce-application), you should lock a specific version of OroCalendarBundle (2.6.0 or 2.6.1) in your custom application with either of the following commands before running composer update:
composer require oro/calendar-bundle:2.6.0
composer require oro/calendar-bundle:2.6.1