Please make sure that you have the latest version of Meta Box and Meta Box AIO. Then deactivate all plugins except Meta Box and Meta Box's extension, switch to the default theme of WordPress (Twenty Twenty One).
Hello
Same here this morning with upgrading the combo Metabox 5.7.2 & Metabox AIO 1.20.2 fatal error. Move the extnsion AIO in a safe place the site is online again... Thanks to fix the problem
Metabox 5.7.2 and just downloaded the AIO 1.21.0 and it has crashed my site. As soon as I rename the AIO the site works. I can't find the older AIO versions on the site so can't roll back either unless I restore a backup...pfff
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