I'm also having trouble trying to load. I'm using an sd2iec with fastload on a C64c. I'll use vice if I have to, but I really don't want to. I don't know what to do with the .crt file. I've only ever used .d64 files.
The game is an EasyFlash cartridge image, so won't work with an SD2IEC device. For testing on real hardware, I use a KungFuFlash cartridge. Else, it'll work on any emulator (including TheC64 mini/maxi).