Please double check the following:

• Is your Step's Robot able to deal with the file you are providing it with? The video related robots, for example, will ignore all files except videos.
• Does the Step referenced in your Step's use parameter produce any result? Are you sure that your Step actually has some input?
• If the result of your Step is passed into a subsequent Step, it will not produce a result by default. You can add result: true to your Step to force the creation of a result in this case.