I've been trying to upgrade Joomla from 3.8.13 to 3.9.0 and got the following error message right, at what appeared to be, the end.
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Fatal error: Cannot make static method Joomla\CMS\Helper\ModuleHelper::getModuleById() non static in class AriModuleHelper in /home/sites/4b/e/eeaee9cda7/public_html/plugins/system/ariphotogalleryanywhere/ariphotogalleryanywhere/kernel/Module/j16/class.ModuleHelper.php on line 75
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I don't know if this error message is meaningful to you or not.
ARI Photo Gallery (including Anywhere and ARI Image Slider are up-to-date whilst Sexy Lightbox is at version 1.11.12 (only just discovered version 1.11.13.)
I would be grateful if you could let me know whether or not ARI Photo gallery Anywhere is causing my problem and, if so, whether there is a fix?
Many thanks David

Hello,

Download the latest version of "ARI Photo Gallery" in "Member Area" on our site and upgrade "ARI Photo Galley" module and "ARI Photo Gallery Anywhere" plugin.

Regards,
ARI Soft

Fantastic. Thank you very much. The Joomla upgrade worked (with much holding of breath as the progress reached the end!)
Thanks again.