This often means the dc_boot.bin file is corrupt or invalid. Re-dump the BIOS.
Modern emulators often use modified or region-free BIOS files to bypass these restrictions, allowing you to play games from any region seamlessly. Common BIOS Issues and How to Fix Them sega dreamcast bios files work
The BIOS (Basic Input/Output System) is stored on the console's motherboard and performs several critical tasks upon power-up: This often means the dc_boot