At the office we recently sent out a load of emails inviting people to a promotional event for a newish charity service. There was a brightly coloured PDF attached with a clickable link leading to an Eventbrite signup page.
About 10% of the successful sign ups came via people emailing me to say they couldn't get the system to work and could I sort if out for them? I just went to Eventbrite and put in their details.
The "audience" for this was people in Local Government, charities and businesses of all sizes. They could all receive and reply to email but for a significant proportion going one step further was a problem.
I'm still not sure where the failure was. Were their systems set up wrong? Or was clicking on an invitation in the place where it said to click too much?
This Internet thing really doesn't work for everyone.