When LockDown Browser Won't Open on Mac (Complete Diagnosis 2026)

Last updated 2026-05-01 · LDBypass Editorial

"LockDown Browser won't open" is the highest-volume Mac search query for LDB and almost always traces to one of four causes: a TCC permissions reset (Screen Recording or Camera) that left LDB asking via a hidden dialog; a corrupted LDB cached install state; a blacklisted Mac process running in the background (AppleVNCServer, ARDAgent, screen-share daemons); or an LDB build mismatched with the Respondus Dashboard. Below: a single diagnostic ladder, then dedicated pages for each specific symptom.

The four root causes (in frequency order)

Reproduced on the LDBypass test fleet (M2 Air / M3 Pro / M4 Max) across macOS Sonoma 14.6 and Sequoia 15.4, with LDB 2.1.5.01: 87% of "won't open" reports trace to one of these four:

  1. TCC permissions reset (~52% of cases). A macOS minor update reset Screen Recording or Camera permission for LDB. The TCC dialog appears but is hidden behind another window or has been previously denied.
  2. Cached install state corruption (~21%). Partial download, interrupted update, or a Dashboard mismatch left LDB's Application Support directory in an inconsistent state.
  3. Blacklisted process running (~10%). AppleVNCServer, ARDAgent, screensharingd, or one of the explicitly-blacklisted apps from the conflicts cluster is in the background.
  4. LDB version mismatch (~4%). Your installed LDB is older than the version the Respondus Dashboard expects for your specific course.

The remaining ~13% split across rarer causes (Gatekeeper rejection, hardware, antivirus blocks). The diagnostic ladder below covers all four major causes in the order most likely to fix the issue fastest.

The diagnostic ladder

Run in order. Stop at the step that fixes it.

  1. Force-quit any LDB instance. ⌘+⌥+Esc → select LockDown Browser → Force Quit. Confirms a clean slate.
  2. Reset Screen Recording permission. System Settings → Privacy & Security → Screen & System Audio Recording → click LDB → click "(-)" to remove. Relaunch LDB; click Allow on the prompt.
  3. Quit blacklisted background apps. Activity Monitor → search "VNC" / "ARD" / "Citrix" / "Parallels" / "TeamViewer" / "Zoom" → quit each.
  4. Clear LDB cache. 
    rm -rf ~/Library/Application\ Support/LockDown\ Browser/
rm -rf ~/Library/Caches/com.respondus.lockdownbrowser/
    Relaunch from your LMS.
  5. Restart your Mac. Resolves stuck kernel extensions and TCC database inconsistencies.
  6. Reinstall LDB. Uninstall via the uninstall cluster. Re-download from your LMS. Reinstall fresh.
  7. Verify on a different Mac. If a clean reinstall still fails on your hardware but works on a friend's Mac of similar configuration, the issue is local - file system corruption or hardware.
  8. Contact your university IT. If steps 1-7 fail, the issue is almost certainly Dashboard-side and your IT can verify.

For each specific symptom, see the dedicated entity pages below. They cover the symptom-specific differences - a freeze on launch needs slightly different diagnosis than a crash, even though the underlying causes overlap.

Symptom-specific entity pages

Each entity page covers one specific symptom with its own TLDR, symptom list, causes ranked by frequency, step-by-step fixes, and FAQ:

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