My World, My Way problem

Ok, so...I was playing My World, My Way rom on my NDSLite.
I use R4i Gold with v1.8 firmware.I went to the town called: "North Town" did everything needed, then when I was going to gate and when the boss is about to appear, the screen goes black as normally it does but it stays black.I was thinking if someone has had the same thing and if someone knows how to solve it.I found other topics about MWMW but as they were really old, I decided to make a new one instead. (none of the topics I found had answer to my problem.)