Visual Composer is a premium plugin which can be automatically updated via a purchase code, not the theme purchase code, but the plugin purchase code.

You don`t have to buy it, because you earned your right to use it for free, within our theme.

Same thing for Revolution Slider plugin.
However, you`re not able to make automatic updates of the plugin, because it requires a license key, which can be obtained only by purchasing it. You don`t have to, because plugin updates are managed by us, with each theme update, before ensuring that the new version is working fine with the theme.

Revolution Slider is a premium plugin which can be automatically updated via a purchase code not the theme purchase code, but the plugin purchase code).
You don`t have to buy it, because you earned your right to use it for free, within our theme.
However, you`re not able to make automatic updates of the plugin, because it requires a license key, which can be obtained only by purchasing it. You don`t have to, because plugin updates are managed by us, with each theme update, before ensuring that the new version is working fine with the theme.

Go to the admin area, login and deactivate all plugins. Afterwards, check your frontpage again. If it loads without error, then you have a plugin conflict and you must start activation each plugin. When that error appears again, it means that the last plugin you activated is the one that needs deactivating. Check the others as well to make sure that it was the only one.
However, if the error appears on the front end and the back end admin area, then you must access the site through a FTP client. Change the name of your wp-content/plugins folder to something else temporarily like “plugins.bak.” This will make WordPress ignore your plugins. Afterwards check to see if this solved the problem. If it did, log into your admin section and then change your plugin.bak folder back to plugins . Deactivate all of your plugins via your admin page.