"Call to undefined method Calendar\Library\Carbon::setWeekStartsAt()" Solspace Calendar I've got Solspace Calendar installed to the best of my knowledge. I have repurposed the 'calendar_demo' files to 'calendar'. Both /calendar and /calendar_demo just show:


  "Call to undefined method Calendar\Library\Carbon::setWeekStartsAt()" in DateHelper.php.


/calendar/week does the same. A path like calendar/2016/11 just give a Twig error.

I can't understand why this is happening. I'll give more details if you ask me, I don't know what else to give.
The issue has to do with another third party plugin (Postmaster) installed and also using Carbon. The Postmaster plugin appears to be using an older copy of Carbon and Calendar is loading Postmaster's Carbon library, causing issues.

Manually updating the vendors directory to use latest versions may resolve this issue. We will try to reach out to the developer of Postmaster and see if they can resolve this on their end. :)

Customers effected with this issue can contact Solspace support for an updated vendors folder for Postmaster that may resolve the issue.