"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. (See the details in this article).
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. (See the details in this article).
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.