We've released a patch that fixes a bug seen in P.U.R.E. 5.2, for users whose hardware cannot compile GLSL shaders at all (Intel chipsets, older ATi / nVidia cards).
Please update to 5.3 to play P.U.R.E. online. This patch can be installed directly to the mods/ directory of your installation of P.U.R.E.- just unzip it there. We'll be issuing a new complete installer for playing the single-player games soon.