To resolve this problem, and resume booting, you'll need to reboot using a QNX 4 floppy disk.
Enter the following command:
dinit -hb
where:
When dinit initializes a disk, it writes a loader in the first block. If the disk is a floppy disk, the loader is the bootstrap loader, else it's the secondary (or partition) loader. If you feel the need to rewrite the loader without reinitializing the disk, you may specify the -b option.