The scph5501.bin file specifically refers to the BIOS file for the PSX (PlayStation) console, which was released in 1994. This file is used by emulators to provide compatibility with the original PlayStation games.
If the error persists even after adding the file, the file might be corrupted. A "healthy" scph5501.bin file typically has an MD5 hash of: 0555c6dae890630573160340a5bc4404 Common Alternatives scph5501.bin missing
If the file is in the right place but still won't load, check these settings: The scph5501