I'm sorry I can't give you better news, but unfortunately you just can't please everyone all the time. I do have a few tips for you, though, on how you can make scheduling woes a little bit better all around.
What Participants Really Want
Have you ever asked your customers about a convenient meeting place and timeframe? If not, now is the time to take a survey. Ask them specifically when and where is most convenient for them. If you've asked before, maybe it's time to re-evaluate with fresh survey information. An attendee's schedule can change drastically from year to year.
You Can Always Take a Direct Approach
Do you provide customized training? Do you go on the road when needed? Then tell them! People like flexibility and choices, so give your potential customers additional options to learn from you or your event.
Map It Out
Nothing is more frustrating than not knowing where an event takes place. Be sure to include all event access information by providing complete transportation information, maps and even free limo service. Make sure your schedule clearly indicates the 'where and when' so that your attendees know at a glance where they want to be.
You can't please everyone, but you can aim for the majority. Remember, most of your attendees genuinely want to be at your event, but there are always conflicts in schedules. Gather your target audience's input then put it into action.