SIGILL error when adding new png files

ExecutionEngineException: SIGILL when adding 20 PNG images I am working on MacOS with the latest Unity version. I am making a 2D grid-based game (something like Candy Crush). Unity is setup for 2D. I started with 3 sprites from png files to fill the grid and it works well. I added 20 new sprites, still PNG files, all 128*128. Each picture shows an icon, and I deleted the background, so it's transparent behind the icon without using an Alpha channel. I use the default settings for the sprites. Now when I run my game, I get this SIGILL error. And if I try to run again, Unity crashes. The problem is obviously coming from the new files, but I can't see a problem with my png files. I doubt that Unity has a hard time handling 20 png. Has any of you any idea about that problem? Thanks!