By the time I finished making "explode view" on the assembly and when I want to add "line sketch explode", there is a little problem that I do not know. When I click OK on the Route Line dialog box, and then I click Exit Sketch, appeared dialog box "This operation requires a fully defined sketch". So I can not see the results of the line sketch. But I just can 'exit sketch', when the line sketch that I have turned into 'fix' on add relations. Please be explained about this. Is the way this is so or there is another explanation?

Thanks