I have faced this issue recently in my current project [Later on, I realized that I was aware of this issue earlier perhaps 3 yrs ago when I was working in the consulting firm, my bad memory:)]. The requirement is to create the calendar event when the record is created in one of our Custom object based on the start and end date fields in it.

I created a process builder and it gets triggered when the new record is created in the Custom object. Immediate action in the process builder is to create a record in Event object.

It works fine when the difference in start and end date is less than or equal to 14 days (duration of the event is less than or equal to 14 days) else it throws an error ”

Vote for the below idea so that salesforce removes this limit in the calendar event:

https://success.salesforce.com/ideaView?id=08730000000Guw6AAC

Workaround: I created a flow to create events based on the start and end date. Suppose, start and end date span for 6 months(Start date=15/5/2018 and End date=15/11/2018), split them into 14 days and create events accordingly. So, in this case, I would have created 13 event records approximately from 15/5/2018.

Please comment below for any questions on this.