It seems to be checking that
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\EnableBalloonTips
is not zero. This is a check done by some library code, it's not something I've written. I could turn it off, but then again, are balloon tips working in Construct 2? Open the parameters dialog and type in some gibberish to make it give a syntax error, and it shows a balloon tip. If it doesn't show a balloon tip it's going to be pretty confusing, so I guess the warning should stay then.