The Lexmark website is far from being a model of clarity but it seems to suggest that people upgrading to Windows 7 should disconnect their printer and uninstall the old driver first, then reinstall the Vista driver. Since you've obviously already upgraded, perhaps uninstalling the Vista (or XP) driver, and then installing the Vista driver (which, according to the Lexmark website, should work under Windows 7) might do the trick?
http://tinyurl.com/ya8acwj