I can't stop scheduled playback!!

Using Decklink.net and DecklinkAPI, I make a application to control scene.

If i don't use StopScheduledPlayback method, It do well.

Until re-use StartScheduledPlayback method, It's not a problem.

But After use StopScheduledPlayback method, and use StartScheduledPlayback method then It's not work.

Maybe I use method incorrect. so I want to know how can use StartScheduledPlayback again without error..

Please help me. I am fury about this problem..