Professionalism or Miscommunication?

My day didn't start right. I'm supposed to be sleeping however, when I saw in my mobile that it registered 5 missed calls and 5 SMS I was thinking it might be urgent so I got up. It so happen that people we sent for external training were having problems regarding the schedule and being an OC-type, it irritated me a lot. Being part of the support group, my priority customers are internal employees. Customer satisfaction is one indicator that I did my job well and 'though it's true that "Complaint is a Gift", still if I can eliminate/avoid it, why not?

So I now ask the question, what went wrong? I spent the past few days coordinating this seminar with the external vendor. Here's what happened:

1. The instructor (who is not the program coordinator) made arrangements with the participants for Day 2. He gave in to their request of changing the time not knowing that there are 3 more participants who will be joining the Day 2 seminar.
2. The instructor did not inform the program coordinator so the latter was not able to inform me as well.
3. When the 3 additional pax came in and asked about the time of the seminar (since they're wondering how come no one's around), nobody in their office can give an answer.

Moving forward, how do you think can I avoid situations like these? I know the answer but I need someone to validate it. Going back to my blog title, is it an issue on professionalism (on the vendor's part) or miscommunication (between me and the vendor)?