Issue with upgrade
I update a very old version of concrete5 (188.8.131.52) to the latest legacy version (5.6.4) to export all content and
I do it manually (replacing the concrete folder and browsing index.php/tools/required/upgrade
This upgrade cause an error of the blank dashboard so I grab the js folder of the old version and replase the js folder of the new version; this fix the issue but now when I navigate to any content page I got the error:
Fatal error: Call to a member function checkLogin() on a non-object in /var/www/concrete5/themes/mytheme/show.php on line 78
5.6 updates need to be run through the /updates/ directory. They can't simply be copied over like in 5.7 or v8. Then run the 'update' in the dashboard. Once update is completed and tested, you can then copy the new core over the existing core, edit the config and remove the /updates/ to tidy up and get rid of old files.
You best bet is to revert to a backup of your site before starting this process, files and data, then go through the safe procedure.