This usually happens when the internal clock is out of sync or the download was incomplete.
This is the #1 error users encounter. The fix is simple but not obvious. Mac Os Sierra 10.12 0 Dmg Download Fix
shasum /path/to/your/InstallMacOSXSierra.dmg This usually happens when the internal clock is
(if known from source) shasum /path/to/Install.macOS.Sierra.10.12.0.dmg shasum /path/to/your/InstallMacOSXSierra
Open Terminal (from the Utilities folder) and type date 0920170016 (sets it to Sept 20, 2016). This "tricks" the installer into thinking the certificate is still valid.
| Symptom | Likely Cause | |--------|----------------| | Download stops at 99% / “Network connection lost” | Apple CDN redirects old versions; timeout | | “No mountable file systems” error | Corrupted or improperly created DMG | | “This copy of the Install macOS Sierra.app is damaged” | Expired or missing certificate (common for 10.12.0) | | DMG opens but installer shows “This version of macOS is too old” | System date wrong or incompatible hardware |
This error often occurs because the app's security certificate has expired or the file was corrupted during download.