I thought is was a wind ON not UP
There is one other possible solution that Sue has just turned up in that it is possible (in the sense that there seems to be at least one instance of it happening) that a badly loaded film can interfer with the shutter and prevent it firing - the silm still winds on, but the shutter is unable to fire. Of course, a simple way of checking this would be to open the shutter on bulb and, with the lens off, just look through the front and see if you could see the film. This would indicate whether the film was making it to behind the shutter, and that the shutter opened.
If the camera only works on bulb, then a few stacked ND and polarising filters might let the wedding be shot on B. Even half a second is long enough to see if you can see film.