LIFE ON TITAN
I'm gweedo and I have been playing Hardwar for a long time. I needed a good challenge, so I looked on your website at the offline challenges and found Lancelot's cop challenge I took up the challenge and had no trouble completing it.
The trick to killing off cops is to hide behind somthing (like a building) when the cop tries to attack you he will only shoot the building you are hiding behind. The cop will usually run into the building you are hiding behind. All you have to do now is blow him away. Generally you never let a cop attack you head on or you will lose. Oh and by the way I didn't get the error message (I am planning on doing this challenge again).