I urgently need help with this custom sprite I made....

[Gimurei]

Hi there! Hopefully I'm posting in the proper board...

As I was attempting to swap Nate's back animations with some sprites I drew, I noticed BWSE couldn't read the file properly and corrupted the image.

I spent an awful lot browsing for solutions, yet I barely found out anything. I understand it probably happened due to me having used colors I shouldn't have, yet as I have no clue what these supposedly "correct" colors are, I can't even make sure THAT's the actual reason... Any suggestions? 

Besides, were I to actually find out what the colors BWSE won't accept are, would there be a way of automatically editing the palette by, say, some sort of compression? 

I beg of you, please give me a hand if you are able to!! :c 

Edited August 31 by Gimurei