@dan Stephens
Verify whether they conflict with iThemes Security plugin.
Do a test in local server, if you are producing this error in local environment then ok.
Very first time when we rename wp-content directory then iThemes Security plugin adds two lines in wp-config.php for identifying directory and site paths. By this time, all the plugins installed will be disabled mode. Admin has to activate once again all those plugins. They will get exact or absolute path to their plugin directory with modified wp-content directory path.
Another issue we experienced that, if iThemes Security plugin fails to write on wp-config.php for absolute path info for modified wp-content directory, all plugins will disappear. In this case, we have to add those two lines of code on wp-config.php. And avery thing works fine.
If you are not having the above two kinds of problems and still you want to revert to the default wp-content directory name, then you have to delete some tables in wp-options table in your site data base. I have mentioned those tables info here in reply to other thread.
