If you tried to join a webinar and hit a "The timestamp signature and/or certificate could not be verified or is malformed" error, that means Windows is unable to update its internal certificate. This can be caused by many scenarios.

1. In the "Error - GoTo Opener" window, click Show log file.
2. In the log file, search for the latest instance of https://builds.getgocdn.com:443/builds/g2m. This file should end with G2MCoreInstExtractor.exe.
   Note: An example of the file is https://builds.getgocdn.com:443/builds/g2m/18705/G2MCoreInstExtractor.exe.
3. Copy the file link and paste it in a new browser to download the file.
4. Once downloaded, open your Downloads folder and find the file you downloaded. Right-click the file and click Properties.
5. Under General > Security, click Unblock and Apply.
   
6. In the Digital Signature tab, click Details.
7. Click Details and View certificate, and make sure the "Valid from" dates have not expired.
8. Click OK.
9. Rejoin your meeting!