I have installed Comodo Free Firewall Version 4.0.138377.779. When I navigate to More–>Manage My Configurations, I find 3 Options, Comodo - Internet Security, Comodo - Proactive Security and Comodo - Firewall Security. At a time, I can only make any one of this active. What is the difference between this and why I am able to activate only one of the option at a time?
These are profiles that alter your security settings.
Think of it as a user profile on a multi-user PC. Each profile has settings specific to each user. You can’t log in more than one user at a time because the settings would likely conflict and the PC wouldn’t know which settings to give priority to.
As for the difference between them, look up Manage My Configurations in the help file. There is a good description of the differences between each configuration.