I’ve just got this error page when trying to generate invoiceplane/index.php/reports/sales_by_client with date format 14-Aug-2017 :
Fatal error: Call to a member function format() on boolean in /srv/data/web/vhosts/site.org/htdocs/invoiceplane/application/helpers/date_helper.php on line 115
A PHP Error was encountered
Message: Call to a member function format() on boolean
Line Number: 115
with date format set as 01.08.2017 the report generates OK.
Hope this help.