Dangling modifiers are cousins of misplaced modifiers, but in this case, the sentence element that the modifier is supposed to be modifying never even makes an appearance in the sentence. For example:
Working through the night, it became impossible to stay awake.
In this case, working through the night should modify something—but what? The writer implies a person, but doesn’t explicitly refer to him or her.
This is a grammatical error. Fortunately, it is easy to fix:
Working through the night, she found it impossible to stay awake.