Check whether the site is in the air for everyone and only you can not sign in, or it's closed for everyone.
1. Install the extension (click "Add to Chrome")
2. Click the extension icon (after installing it).
3. In the pane that opens, click "Check" to check the open site in the current tab, or paste in the text field the URL of the site, then click "Check"
4. You will be asked if the site is open for other people, closed for everyone, or you are not connected at all to the network.
For more instruction visit the website: https://1ce.org