This was the error code I got:
The game crashed whilst mouseclicked event handler
Error: java.lang.NoClassDefFoundError: net/coderbot/iris/gui/screen/ShaderPackScreen
Exit Code: -1
You are running Pupil Magnesium version without Pupil. Download regular version and the issue will be fixed.
Pupil is unreleased for now. You need to wait to use this version.
This was the error code I got: The game crashed whilst mouseclicked event handler Error: java.lang.NoClassDefFoundError: net/coderbot/iris/gui/screen/ShaderPackScreen Exit Code: -1