"schedule an appointment" service at uscis.gov is not

available any more? why i got this message when i clickschedule an appointment, then clickclick here for English? the following message is what i got:

There is a problem with this website\'s security certificate.


The security certificate presented by this website has expired or is not yet valid.

Security certificate problems may indicate an attempt to fool you or intercept any data you send to the server.
We recommend that you close this webpage and do not continue to this website.
Click here to close this webpage.
Continue to this website (not recommended).
More information


If you arrived at this page by clicking a link, check the website address in the address bar to be sure that it is the address you were expecting.
When going to a website with an address such as https://example.com, try adding the \'www\' to the address, https://www.example.com.
If you choose to ignore this error and continue, do not enter private information into the website.

For more information, see Certificate Errors in Internet Explorer Help.