Thanks for the question. The following article outlines the exact error message you described, and a potential resolution:
Sorry Matt. It wasn't a user problem of clicking more than once. I followed instructions posted by Netdude21 and this is what worked:
Go to the folder /Applications then right click on FaceTime.app go into /Contents/LaunchAgents and look for two files "com.apple.imagent.plist" and "com.apple.apsd-ft.plist" and copy them into your /Home/yourusername/Library/LaunchAgents. If you can't find "com.apple.apsd-ft.plist" do a Google search for it and download it, the name will be "com.apple.apsd.plist.txt", do a cmd-I on it and rename it "com.apple.apsd-ft.plist" put this file in the same folder as "com.imagent.plist", launch FaceTime and if your webcam lights up, your good to go.
I didn't have to download any files or rename them. I simply followed the first part of the instructions and copied "com.apple.imagent.plist" into my /Home/yourusername/Library/LaunchAgents and everything worked after that.