When the warning appears, "Update server is not supplying information, or the connection to update server is blocked. Please try again later" this typically indicates that security settings or another application is blocking access to the Respondus servers that LockDown Browser uses at startup.

When LockDown Browser starts, it must be permitted to access this server: static-public-downloads-cloud.respondus.com

LockDown Browser accesses this server in order to check if an update has been issued by Respondus. If your computer and/or network is blocking access to this server, the LockDown Browser session will not be permitted to continue.
It's possible that your computer's security settings are blocking access, or you possibly have a firewall or anti-virus software running on your computer or network that is causing the block.

What to do next:

1) Temporarily relax all anti-virus and firewall software on the computer and try the exam again.
2) Reset your computer's internet options.  For Windows users, go to control panel and select "Network and Internet." Once there, click on "Internet Options".
On the "Security" tab, ensure that your settings are not higher than "Medium". On the Advanced tab, click "Reset" located under the header "Reset Internet Explorer Settings". In the window that opens, select "Delete Personal Settings" and then click on the Reset button. Doing this will impact all client browsers, not just Internet Explorer.

After resetting the internet options, you may need to restart your computer.

3) Once you reset your internet options, you should also ensure that TLS 1.2 is enabled on your Windows computer. If not, it can cause the error. You can check this by going to:

Control Panel > Network and Internet > Internet Options > Advanced tab.

Scroll down until you see "use TLS 1.2" and make sure it is checked.

4) If the problem persists after steps 1-3 above, the problem could be caused by your computer, ISP, or network blocking access to the Respondus servers. These servers include:

server-profiles-respondus-com.s3-external-1.amazonaws.com
static-public-downloads-cloud.respondus.com
www.respondus.com
help-center-respondus-com.s3.amazonaws.com
smc-service-cloud.respondus2.com

For Windows: These domains may need to be added as "trusted sites" in security settings on the local computer and possibly also to network firewalls or routers. To add these domains on your local Windows computer, go to Control Panel Network and Internet and click on "Internet Options."  Navigate to the Security tab, then "Trusted Sites".  Add the above domains to your computer's trusted sites list.

For Macs: it's possible the domains are being blocked through parental Controls, third-party security programs, or network/ISP blocking.

5) If the problem persists after following the above steps, try using a different WiFi network.

6) Finally, if a deadline for an exam is near, you may want to consider using LockDown Browser on another Windows or Mac computer. This will also help to determine whether the issue is specific to your computer or a broader issue that needs further investigation.