Just happened to me on a FM10... A lever disengaged at the bottom of the camera probably because somebody tried to rewind without pressing the rewind pin.
... You have a problem with the double wind prevention lever, located under the baseplate. Either the "hook" on the end of the lever is bent slightly, or there
Anyway, got an FM2n coming that has an issue with it. You can continue to advance the film without firing the shutter. According to the shop I'm getting it
Hi Shahrukh, FM is a great camera, have one, have had three in 30 years. Thought I had what you asked for but could only find user's manual and a .pdf about