This is because your Kongregate account is not a valid login through the Client version, you would need an account created through http://www.brick-force.com (the official site) to log into the game client.
1) We can't have players make custom skin because it can be abused, like they did when we allowed people to make their own map and upload them. 2)Anti-Hack, it easier said than done - Igor is the only programmer, it is a lot of work for one person. 3)We are still in the process of adding guns but Igor is handling #2 first. 4) We'll see ;) 5) I don't know what the source of that problem I will let you know when I do. 6) YES!! I want that too, but Igor is by himself so let him do #2 first then worry the rest afterward.