No but I can only guess. It's not installed in your user account. You don't have permissions to use the program by the admin of the comp. Else your firewall is not configured: Did you configure your firewall so it allows LW full access (advisable not to have 2 active firewalls b/c they can interfere with each other); Firewall configuration instructions (click on link)

You may have anti-spyware, anti-virus, etc. programs that need to be given permission in their options for LW to run. Else, you're using it at work or school where such a program doesn't have clearance to open/operate.