When you use LOAD IMAGE you're loading the image directly into the program. When you use LOAD BITMAP the number at the end is the bitmap number which creates that bitmap at the resolution of the file loaded and switches to that bitmap as the current working screen. Image #1 is already loaded in memory so you don't need to grab it... but since you use LOAD BITMAP you do need to put down SET CURRENT BITMAP 0 to change the current working screen to the main view screen... otherwise you'll be stuck working on a screen the user never sees.
Here's what your code is doing... see attached image too:
SET DISPLAY MODE 800,600,32
` Load image 1 in memory
Load Image "arena.bmp",1
` Create bitmap #2 and switch to bitmap 2 as the current working screen
Load Bitmap "sumowhite.bmp",2
` Create bitmap #3 and switch to bitmap 3 as the current working screen
Load Bitmap "sumoblack.bmp",3
` Get image 1 from current working screen (which is bitmap 3)
` If bitmap 3 is smaller than what your grabbing then it'll produce the error you see
GET IMAGE 1,1,1,383,383
` Show sprite (since still on bitmap 3 you won't see anything).
Sprite 1,0,0,1
wait key
