As said in my PM to you, it's most likely the BG3 (snow), which your Emulator seems to be unable to handle.

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NEW! SMW2 Yoshi's Island is done!
Last update: 2012-12-31

I don't know if anyone is still active in this thread, but I have been trying all night to get this patch to work. I have tried to aquire the appropriate Roms from multiple sources and apply it to. I've tried to look through the thread here for help but no matter what I do or which file I try to patch. I just get the same error message when launching snes9x

"NEW! YOSHI'S ISLANDd__" [bad checksum] LoROM, ROM, NTSC, SRAM: 0kbits, ID:Hack, CRC32:4913E01D

The emulator plays all my other Roms fine, so I doubt the problem is with it.

This is pretty much my last shot before giving up for good. I've tried everything I can think of but nothing seems to do the trick, and apparently nobody else seem to be having trouble.

Easy way to tell if headered or unheadered:

Go to properties and look at the exact byte count of the file.

Unheadered: 2,097,152 bytes
Headered: 2,097,664 bytes

Notice that headered has 512 bytes more at the beginning, whereas an unheadered YI ROM will begin with byte $78 (which is SEI instruction).

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wiki

Hello all, I'm new to the forum!

I just completed a 100% semi-TAS of NEW! SMW2.
I think this is the best romhack of Yoshi's Island to date, but a real TAS is unlikely to happen, so I decided to do one myself.
IMO, it's definitely a very interesting watch.
I highlighted the best levels in the video description, so feel free to look at them if you don't have time or just simply don't want to watch the entire thing.

Enjoy!

https://www.youtube.com/watch?v=a0SaHJljFeg

nice dude, i'll share this around

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wiki