As requested by your standard email support (who redirected me to the forum after my direct reports), I am posting this critical bug fix publicly so your development team can easily spot it and implement it.
The Issue:
When trying to create or edit an article on Joomla 6.1, the system throws a Fatal Error, breaking the page completely.
The Cause:
The error is caused by a deprecated class call in your core files. SP Page Builder is still using the old Joomla framework syntax for file checking.
Error: Class "Joomla\CMS\Filesystem\File" not found
The Fix:
File: components/com_sppagebuilder/builder/classes/base.php
Line: 255
You simply need to change this old syntax:
if (File::exists($admin_file))
To the standard native PHP function (which you already use in other parts of the same file!):
if (file_exists($admin_file))
Please include this one-line patch in the very next release. Currently, the only workaround to use SP Page Builder on Joomla 6.1 without crashing is to force Joomla's "Backward Compatibility" system plugin, which is not an acceptable long-term state.
