OK. Time to check Dr. Google.
GOTO:
https://discussions.apple.com/thread/7677001?start=0&tstart=0
It describes a posted solution to your problem (but under Sierra, not High Sierra).
You will need to use "Terminal" app to remove the Calendars directory, like so:
> rm -f ~/Library/Calendars
The contents of my Calendars directory show:
097954DB-FC81-414D-BEC5-4EA43BBF4B9D.caldav
2CD0A3E7-17A2-4088-A363-D6B2C02411EF.calendar
3EE4262B-AF6A-42C8-8CAA-7E8E09A61314.calendar
4818311A-1DEF-41DD-909E-B7E4687C8866.calendar
C90DB439-C09E-45A6-830B-9699B983A5D3.calendar
Calendar Cache
Calendar Cache-shm
Calendar Cache-wal
Calendar Sync Changes
Calendar Sync ClientID Conflicts.tmp
Calendars and Reminders 1.11.13 10.53 AM.icbu
Calendars and Reminders 3.24.13 10.11 AM.icbu
E2CED9C7-6BB2-4F3A-AF5D-C58E4296317B.exchange
E5088755-FCE7-4174-9E2C-277693053E31.calendar
Email Cache.plist
F0AC5EB4-0208-46CE-99AF-554175B64F95.group
Incoming
Pending Events
[Pretty drastic if you have not sync'ed your Calendars and Reminders with iCloud, and you care for their contents, like the OP.]