LockDown Browser Error A4 on Mac (Update Check Failed Fix)

Last updated 2026-05-01 · LDBypass Editorial

What error A4 means

Error A4 fires when LDB's startup update check (a request to updates.respondus.com or similar) fails within the timeout. LDB is conservative here - it will not launch the exam if it cannot verify whether an update is required.

Mac-specific causes

• VPN blocking Respondus's update endpoint.
• Captive portal not yet authenticated (university Wi-Fi often requires re-auth at exam time).
• macOS firewall or Little Snitch denying outbound to *.respondus.com.
• ISP-level filtering or rate-limiting.
• Respondus servers experiencing momentary issues (rare but reported).

Fix 1 - Disconnect VPN and retry

Most common fix. Disconnect any active VPN (corporate, consumer, university). Wait 10 seconds. Relaunch LDB.

Fix 2 - Authenticate captive portal first

If you're on university or hotel Wi-Fi, open Safari and visit any HTTP site to trigger the captive portal sign-in. Complete the sign-in. Then relaunch LDB.

Fix 3 - Whitelist Respondus in your firewall

Allow *.respondus.com on TCP/443 in Little Snitch / Lulu / macOS Application Firewall. See conflicts cluster for procedure.

Fix 4 - Test with cellular hotspot

If A4 persists on your home Wi-Fi but works on cellular hotspot, your home network is the problem. Use cellular for the exam window.

Fix 5 - Reinstall LDB if all else fails

Run the complete uninstall (uninstall cluster) + fresh install from your LMS link. The fresh install bypasses the update check that A4 fails.

If none of these work

The remaining cases trace to your specific course's Respondus Dashboard configuration - your university IT or instructor needs to look at the server side. Contact them with: the exact error code, the LDB version (right-click LDB.app → Get Info), the macOS version (About This Mac), and the time of your launch attempt.