In the process of upgrading the statistics charts in the latest release (3.3.6), code has been used that is not valid for PHP version 5.6 or earlier. I was not clear about this when the release was announced.
Whilst it is possible to change this to ensure such backwards compatibility, I am very conscious of this statement from the developers of PHP:
The developers of PHP are no longer supporting PHP 5.6. There will not be any more security updates to PHP 5.6, there will not be any more bug fixes to PHP 5.6. You should not use PHP 5.6 (or any version of PHP 5) in a production environment. Jan 7, 2019
Therefore I have decided instead to declare that kiwitrees is no longer compatible with versions of PHP earlier than 7.0, with effect from release kiwitrees 3.3.6.
Important note:Kiwitrees 3.3.7 is not compatible with PHP 7.4