Refer to this post.
https://community2.invoiceplane.com/t/topic/5156/12
The code in question is this 
$date_time = date_create_from_format("d M,Y", $this->input->post('statement_date_created'));
$statement_date = $date_time->getTimestamp();
$date_time returns a DateTime object. It is possible that the value supplied to first statement above was either incorrect on in a different format than expected. This will cause the built in PHP function date_create_from_format() to return false.
I should probably add a check for this.