Are you running Windows 8?

If not, it's most likely another program is conflicting with GunZ. One example is Game Booster. Checking out this thread may help you: http://www.aeriagames.com/forums/en/viewtopic.php?t=1915295

Tearfulplace wrote:

Fixed. It was a d3dgear or i forgot what its called screen recording program messing with n protect.

Well i went to see if any games or programs i'v installed that night may have something to do with it and it wasn't TF2 or steam so it had to have been the Video recording software and sure enough...When i checked into their technical help for recording games the program has issues with N Protect. So had to completely un install. And it was never running when Gunz was i even tried to find it running in the back round in task manager and nothing it was weird.

Yea i'v noticed lots have this problem they will probably have to do what i did and see if any program has problems with N Protect.

WellOfCourse wrote:

this happened to me, let me show you how to fix this

Game booster closes gameguard, open task manager and CLOSE GAME BOOSTER.

Some anti-virus still block gameguard even if they are TURNED OFF, so open TASK MANAGER and CLOSE the ANTI-VIRUS.