Well start with this:
Turn off fire-wall and anti-virus, reinstall completely (delete leftover folders/files after uninstalling), update through gunzlauncher.exe, which is found in the gunz folder, or update via aeria ignite.
Close background applications such as game booster, itunes, msn, aim, etc as these may conflict with gunz.
When was the last time that you were able to play gunz successfully?
Does GunZ crash regardless of game mode/type or is it only during blitzkrieg / big games?
Try updating your drivers (mainly video card drivers - you can do this with start->control panel->hardware->Device Manager->Find your video card->Right click->update->choose automatically)