This is a very common error. Your Teamspeak 3 server doesn't have the proper permissions to allow third-party add-ons and widgets to access it, but most TS3 servers aren't configured to allow those permissions initially anyway!
You can change this within the Teamspeak 3 client fairly easily, though. First you'll need to enable the Advanced Permissions System:
- Click 'Settings'.
- Click 'Options'.
- Click 'Application' on the left sidebar.
- Click the box next to 'Advanced Permissions System'.
- Click 'OK'.
Now that you've enabled Advanced Permissions, you need to actually add the permissions to your server! This can be done on the 'Server Groups' tab:
- Click 'Permissions'.
- Click 'Server Groups'.
- Click 'Show names' from the dropdown near the bottom of the menu.
- Choose 'Guest' from the left column.
- Add the following permissions to the 'Virtual Server - Information' category:
- Add the following permissions to the 'Group - Information' category:
Once you've done this, make sure that the permissions are allowed (by doubleclicking their names) and you should be set!