"Update server is not supplying information, or the connection to update server is blocked.”

This issue is caused by: Security settings or another application is blocking access to the Respondus servers that LockDown Browser uses at startup.

To solve this issue, please follow the below steps:

1. Temporarily turn off all anti-virus and firewall software on the computer and try the exam again.
2. Reset your computer's internet options.
3. If the problem persists after steps 1 and 2 above, the problem could be caused by your computer, ISP, or network blocking access to the Respondus servers.
4. If the problem persists after following the above steps, try using a different WiFi network.
5. Finally, if a deadline for an exam is near, you may want to consider using LockDown Browser on another Windows or Mac computer. 

For more details, please refer to this article.