A DSM update or Synology restart broke the PATH settings again and made cpio unavailable from the $PATH.

This executable is required for the Crashplan package: it needs it to unpack an update.

Googling found me this post where the solution was to copy cpio from within the Crashplan distribution but cpio is already available in /opt/bin/cpio making the solution even easier by just setting the PATH to include /opt/bin. (as it should so tools like ipkg are available)