SBCL 2.5.1 WIndows 10 I can't determine the source line of that error, but suspect a problem with spin buttons "C:\Users\user\quicklisp\setup.lisp" To load "cl-cffi-gtk": Load 1 ASDF system: cl-cffi-gtk ; Loading "cl-cffi-gtk" .......................... To load "cl-portaudio": Load 1 ASDF system: cl-portaudio ; Loading "cl-portaudio" . debugger invoked on a FLOATING-POINT-INVALID-OPERATION in thread #: arithmetic error FLOATING-POINT-INVALID-OPERATION signalled The current thread is not at the foreground, SB-THREAD:RELEASE-FOREGROUND has to be called in # for this thread to enter the debugger.