• Missing bootstrap compiler or wrong FBC path.
• Wrong host shell for the script being run.
• MSYS2, Cygwin, and Windows paths mixed in one command line.
• Target triplet does not match the installed cross toolchain.
• Old generated objects remain after a platform, backend, or bootstrap change.
• Android SDK/NDK tools are installed but not on the path expected by the script.
• Installer tests pass in-tree but fail from an installed layout because a file was not packaged.

Use the build script for the platform when one exists. If working directly with make, clean only the affected output directory first. Save full clean rebuilds for cases where platform identity, bootstrap output, or generated headers have changed.