PICSimLab Won’t Open on macOS? Gatekeeper and Wrong-Build Fixes

You downloaded the new native macOS build of PICSimLab v0.9.3, dragged it into Applications — and macOS will not open it: a warning dialog, a refusal, or nothing at all. Almost every case is one of two things: Gatekeeper doing its standard job on an internet-downloaded app, or the wrong one of the two .dmg builds for your Mac. Both are quick to fix.

Symptoms

  • Double-clicking PICSimLab shows a dialog saying macOS cannot open it or cannot verify it, and the app never starts.
  • The app icon appears in Applications but launching it does nothing, or it quits immediately.
  • A message suggests the app is damaged and should be moved to the Trash.

Why it happens

Gatekeeper. This is standard macOS behaviour — general Mac knowledge, not a PICSimLab-specific fault: the first time you open an app downloaded from the internet, macOS checks it and, for apps that arrive outside the App Store, asks you to confirm the first open explicitly instead of just double-clicking. A plain double-click can therefore look like a refusal even though the app itself is fine.

The wrong .dmg for your chip. PICSimLab v0.9.3 ships two macOS builds, and they are not interchangeable: PICSimLab_0.9.3_260920_macOS_26.6.1_x86_64.dmg for Intel Macs and PICSimLab_0.9.3_260920_macOS_26.6.2_arm64.dmg for Apple Silicon (M-series) Macs. The arm64 build cannot run on an Intel Mac and vice versa — picking the wrong file produces exactly the “won’t open” symptom with no useful explanation. Both files, with sizes and SHA-256 checksums, are listed on our PICSimLab for macOS page.

An incomplete download. A truncated .dmg (interrupted download, proxy interference) can trigger the harsher “damaged” wording from macOS. That message is macOS’s generic response to a file that fails its integrity checks — re-downloading, not repairing, is the fix.

Fix

  1. Check your chip first. Open the Apple menu → About This Mac. An Apple M-series chip means you need the arm64 .dmg; an Intel processor means the x86_64 .dmg. If you installed from the other file, delete that copy and download the correct one from the macOS download page.
  2. Verify the checksum before you bypass anything. In Terminal, in your Downloads folder, run shasum -a 256 <file>.dmg and compare it with the value on the download page: 46cae7379b3828d771feefcaeb040f87d02ffbd5bd160dcda6152c8fa14b8b00 for arm64, cb6af4651fe811dab3088667f34f3d0495960ec6b0bb4627f44f73a21386d07b for x86_64. Only proceed past Gatekeeper prompts for a file whose checksum matches — that is what makes the next step safe.
  3. Install cleanly. Open the .dmg and drag PICSimLab into your Applications folder, then eject the disk image.
  4. Open it the Gatekeeper way: right-click → Open. In Applications, right-click (or Control-click) PICSimLab and choose Open, then confirm in the dialog. This explicit confirmation is the standard first-open path for downloaded apps.
  5. Or use Open Anyway. If the app was blocked on a previous attempt, open System Settings → Privacy & Security, scroll to the note about PICSimLab being blocked, and choose Open Anyway, then confirm once more.
  6. If macOS insists the app is “damaged”: delete the app and the .dmg, re-download the correct build (step 1), verify the checksum (step 2) and repeat. A verified, complete file does not produce this message; do not go hunting for settings to disable the check instead.

After the first successful open, PICSimLab launches normally from Applications like any other Mac app — the confirmation is a one-time gate, not a per-launch tax. Our macOS installation guide covers the same steps in install order.

Still stuck?

Redo the sequence with the step-by-step macOS installation guide and the file table on the macOS download page. If a checksum-verified build for the correct chip still will not open after the right-click Open on v0.9.3, report it — your Mac chip, the exact dialog text and the macOS version included — on the project’s tracker: github.com/lcgamboa/picsimlab/issues.

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