If your PC Sim initiates a party, you get goals (so if your PC Sim ask a NPC Sim on a date, you should get goals). The welcome party on the other hand seems to only get a time since they are basically initiated by the NPCs. NPC initiated parties don't have goals, only a timer.
The message that the party failed is a bug, that already has a thread though.
So, I hope I understand you correctly (English is not my mother tongue), that you had an event where your played Sim invited someone else on a date (PC or NPC doesn't matter) and you didn't get goals on that ?
It's all about if you invite someone or if you get invited
EDIT: Sorry, posted this before I saw your answer. Above still applies though