This error has multiple causes.

1. (Most likely) BuzzTop has limited coverage in our supported regions. What that means is that there are certain areas in these regions where we cannot help you figure what buses to take to take you to your destination, hence the error.
2. The time you specify to depart at. In some regions, buses do not operate on a 24hr schedule. Therefore, there are times at which buses do not operate, hence the error. To specify which time to depart at, tap the "Leave .." button above the error message.