Apple Calendar gives error message box (with screencast)

My Apple Calendar gives error message like below. And there is an exclamation mark near iCloud. The system is OS X Yosemite (Version 10.10.5).

Does anyone know what is going on here? Thanks!
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You should not post your ID on EE or any public site.
Suggest you ask for a moderators help to resolve this.
 https://[my ID][my ID]/principals/

Try completely signing out of iCloud and then signing back in.  backup all related data before turning off iCloud sync

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This can happen if your reminders list and calendar list have the same name. Make sure the Calendar and Reminder List have DIFFERENT names.
condor888Author Commented:
Although the problem was gone some how, I still appreciate the comments.
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Mac OS X

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