Looks like you're playing a jump map. Most of those are actually made for Quake2, not Paintball2, so they use the Quake2 textures. Those textures aren't included with Paintball2.
just a question, why aren't they included? Wouldn't it make sense that Quake2 textures are included for the jump maps when you download the game, it would really benefit this game by presenting at least some decent textures, rather then no textures. Majority of new players will think bad about this no textures thing and there oppion about this game will be "this game suckZ", remember presentation is one of the most important factor in attracting new players.
There are more players who play in the jump servers then there are in pubs.