Hmmm, perhaps one of those files that you unzipped previously has made a change or two to your system. I read that a lot of .zip files are infected.

The error message has nothing to do with LW. Either the setup file is corrupted (a common occurance) or your system is compromised. It's probably the former, but if you keep opening .zip files that you get from unknown sources, you're guaranteed to infect your computer.