The most common reason for this error is that the file is in the wrong folder on your SD card. The 3DS Homebrew Launcher looks for specific files in the root directory (the base level of the SD card), not inside other folders.
"Failed to open SafeB9SInstaller.bin" typically occurs when the required installation file is either missing from the SD card or placed in the wrong directory Incident Report: SafeB9SInstaller.bin Failure File Missing or Misplaced Critical (Blocks Custom Firmware installation) 1. Immediate Root Causes File Location: SafeB9SInstaller.bin file must be located on the failed to open safeb9sinstaller.bin