Calendar permissions are not working properly. An end user may not be able to edit calendars they have access to.
The calendar the end user is trying to access may not be within the same environment as the user. The user on Premise cannot access a user's mailbox that is on O365. They must both be on Premise or O365. Read only rights will be available to share calendars and full designation rights.
- If Permissions are not working properly, please use the workaround below:
Navigate to File > Account Settings > Account Settings > Change > More Settings > Advanced Tab
Uncheck the box
If the end user is unable to edit a mailbox they have access to, rebuild the user profile and rename the .ost file.
*NOTE: Please be sure to note any .pst files or connected mailboxes so you can restore these as well.