Sounds like someone had a bad link they tried to use. A login-bypass link would end in ciwweb.pl, followed by a ? to indicate that the URL has ended and additional info is being included for the page. We pass in the study name and any additional variables. So, if the full link would have been something like www.mysurvey.com/cgi-bin/ciwweb.pl?studyname=pizza&respID=1234 it's possible that maybe they tried to copy and paste and only ended up with www.mysurvey.com/cgi-bin/ciwweb.pl?studyname=piz
"Piz" isn't a valid study, so it would make an error like this and say "The study name passed in (piz) does not match the study name.
Further evidence that this one was a one-time goof is that you had 29 people use the link and take the survey without issue, and you should be able to take it currently without generating an error.