command-line tool is often more stable than the SAK GUI. You can run nsz -D filename.nsz in a terminal to decompress. Conversion via XCI
Before doing anything else, confirm the file is not partially downloaded. sak decompression failed
SAK cannot decompress anything without the right "handshake." If your title.keys are outdated or missing, the process will fail immediately. command-line tool is often more stable than the SAK GUI
Opened a 10-year-old .sak backup from a dead NAS drive. Error: "SAK decompression failed" instantly. Solution: The drive had bad sectors exactly on the header block. Using GNU ddrescue to clone the drive sector-by-sector recovered the missing header bytes, allowing the decompressor to read the file. sak decompression failed