Deactivate the Plugin Firewall. If the Revolution css editor works then create this Plugin Firewall whitelist rule: /revslider/rs-plugin/css/captions.php in the Plugin Firewall whitelist text area.
Plugin Firewall Manual Setup Steps
1. Copy and paste plugin scripts/whitelist rules to the Plugins Script|File Whitelist Text Area.
2. Click the Save Whitelist Data button.
3. Click the Create Firewall Master File button.
4. Select the Plugin Firewall BulletProof Mode Radio button.
5. Click the Activate|Deactivate button to activate the Plugin Firewall.Each plugin script/file path that you add MUST be separated by a comma and a space. Example: /some-example-plugin/api/paypal-ipn-script.php, /another-example-plugin/some-example-script.php. The path name starts with the plugin folder name (do not add /wp-content in the path name). After manually adding your script/file name path to the Plugins Script|File Whitelist Text Area you would then click the Save Whitelist Data button to save your Whitelist data to your database, click the Create Firewall Master File button and activate the Plugin Firewall BulletProof Mode.