List of helpful tools for visiting out participants in case of any problems:
Checklist
WLAN access data of participant available?
Wifi reception good enough?
Double check crypto key and SSID
if Wifi fails, install DLAN
Check internet access of flukso via ssh and ping.
Inform the participants, what has been done.
Explain what the problem was, what you have done and why it's now working.
Adjust your level of technobabble to the level of the participant's understanding (If they absolutely have no clue about computer stuff, compare the problem with something out of their daily life. They'll understand and feel good.)