Well, first of all, the link you've wrote above it wrong (I guess you are talking about example with 3rd person camera and aimnig at the center of the screen). About the error you've got, you've made something wrong and there is no doubt, cause the example itself (even if it's terrible and very basic) works without any problems. Yet, I can't see a reason for you to create this thread, you want to ask someone to look throw your code and fix it for you? I'm pretty sure, no one will do that...

Edit: on the second thought, I think (if weapon disappears) you've probably deleted it.. yet there are some functions looking the the weapon model, but as it doesn't exist any more, you get pointer error. Don't just copy&paste the code, that won't help you to create something playable, go throw it and learn. Better ask for explanation, then doing something like that..

Greets