That error message was definitely about the ClickOnce service crashing, most likely due to a corrup application cache. This is a Microsoft issue, but unfortunately, it affects Inquisit which depends on ClickOnce.
As Dave mentioned, you can instruct the participant to try one of the other links for the ActiveX, Java WebStart, or Mozilla Plugin versions, in which case ClickOnce is not used.
We also have a utility program that will clean out the ClickOnce cache that you can point your participants to if they see this problem. The utility can be downloaded here:
http://www.millisecond.com/download/win/iqclean3.exe
Regards,
Sean