You'll need to use the normal 'picker' to load that software.
I am using MESSUI. What is the "normal" picker you're referring to? How do you use it?
Which version of MESSUI are you using?
Are you able to load the SNES images by using the "Device View" > "SNES Cartridge Slot"?
What is the content of your snes.zip (BIOS/checksum)?
Basically, the SNES images are working on MESSUI.