On Webex, if you are using a Mac, you can only join one meeting at a time.  If you do not officially leave your previous meeting before attempting to enter another meeting by clicking the Leave red X icon, you will receive this error message:

If this happens, follow these steps:

1. Close the current meeting window with the error message.

2. Go back into the previous Webex meeting you had exited using the link or invitation provided. If you were invited to the meeting, please check your Webex meetings calendar, email, or your Brightspace course page for that information if it was a class session.  If you aren't able to find that information, you may be able to fix the issue without it. You should check your settings to see if you have accepted the Webex plug-in for Safari.  The steps for how to check this are here.

3. Exit this meeting using the Leave red X icon, and then select Leave Meeting in the pop-up window.

4. Re-enter the new meeting using the link or invitation provided.

If it was a meeting you hosted that you cannot close, apparently that is a known issue with Webex.  You can contact Webex support to get them to end the meeting for you.  You can contact them by following the steps here, and they require some information to be able to help.
Information you need to provide when contacting support:
  • Email request from the Host / Partner Support / Cisco Webex Meetings Site Admin / Customer Success Manager (CSM)
  • Original meeting URL if available (Example: cisco.webex.com)
  • Topic 
  • Meeting or session number 
  • Date and Time of session