- is a problem. You have 1.5 megabytes left? On system that has 512 megabytes? Aw...
But I doubt that that's causing your problem. Here are some other ideas.
a) find out if the pfx shows up in the alpha channel. If it does, you have a shading problem. If not, check that Enable stroke rendering is on in the Render Settings under Paint Effects Rendering Options.
b) if it's a shading problem, check that the pfx is illuminated; if there are no lights in the scene, make sure Enable Default Light is on in the Common Tab of the Render Settings.
c) see if another default brush renders correctly. If it does, check your brush. Make sure Modify Color is on (under Channels)