Black Screen Bug- Need Help

It can be various things. It might be an event bug if you have touched events or it could be an ASM bug if you have applied a patch for a headerless ROM on a headered ROM. If the blackout happens after the fight, when the screen load, you could use Geiger's debugger and set a breakpoint on the map loading routine and see from there where the code goes into error. You could also revise the event after the battle to see if the event code in the ROM matches the event dump.