Have you Received an error where one of your calendar items are throwing weird errors? Does the error read along the lines of "One or more items in the folder you synchronized do not match"? And Does it look like this?
Well look no further, use the below article to quickly resolve this issue and get back on your feet!
Step 1
Open the "Calendar" pane in Outlook, and right-click the "Calendar" folder.
Step 2
Select "Properties".
Step 3
On the "General tab", select "Clear Offline Items".
Step 4
Select OK (Do Not Panic! Outlook will re-sync the calendar and repopulate your calendar folder with the calendar items on the server.)
Step 5 (Optional)
If you notice your Calendar isn't syncing after the above steps, ensure your calendar is selected, then open the "Send / Receive" Tab and pick "Update Folder". Now wait for the system to repopulate your calendar: