Solution:
After completing each troubleshooting step below, test whether you can access your Webex site:

1. Clear your temporary internet files and cookies, see:   
   • WBX38898 - How Do I Clear My Cache and Cookies in Mozilla Firefox?
   • WBX38899 - How Do I Clear My Cache and Cookies in Google Chrome?
2. Exit all instances of your web browser and launch a new copy.
3. If possible, restart your Internet connection.
4. Flush your DNS cache, see:
   • WBX18967 - How Do I Perform a DNS Flush from DOS Command Prompt?

If you are still unable to access the site, contact technical support.  For help, see: WBX162 - How Do I Contact Webex Customer Services or Technical Support?

Verify that your IP address is not on the Bright Cloud or Talos bad IP list (both BrightCloud and Talos should be checked)
Note: You can find your public IP address by visiting https://www.whatismyip.com/

Bright Cloud:

1. Navigate to https://www.brightcloud.com/tools/url-ip-lookup.php#
2. In the Look up URL or IP field, enter your IP address.
3. Check I'm not a robot box and click Look up button.

Talos:

1. Navigate to: https://talosintelligence.com. 
2. In the Reputation Lookup field, enter your IP address and press Enter.