It was Mutex. http://forum.world.st/How-to-resurrect-an-unrepsonsive-image-tp4168518p4178653.html
I remember reading somewhere that Monitor was broken in Pharo/Squeak?
I do not remember where.
Does anybody have experience with bad monitor behavior?
Because we got some bad experience with Monitor.
THe funny part is that now doing self inform: freezes to death our image.
Stef