[GT] [LD] How can I complete "I want to have an unforgettable dance party!"?

Hello,

Apparently I had my out-of-experience sim hosted the dance party at the chalet garden and then the cliff at Windenburg but for no reason I can't complete this unfinished business. I did not even end the event early. I really made the sim hosted the party at the lot in WDB as instructed. 

Is there a bug going on with this? Please tell me hoe can I complete this?

Thanks!