Particles Not Rendered In Middle Of Screen?

I am having an issue with the rendering of particles from a Shuriken particle system. There is a circle in the middle of the screen where they are not rendered, even though everything else is.

Details:

There is one particle system located at (0,0,0). At its start, it creates 1000 particles at the perimeter of a radius 1000 sphere. These particles are meant to look like stars (space game), and it gives a pretty nice effect.

However, when my camera is angled closer toward the particle system origin, there is a circle in the middle of the screen where the particles are not rendered. The circle at its max has a radius of about 150 pixels. As I turn the camera away from the center of the particle system, the radius of the circle shrinks, though it stays in the middle of the screen. When the camera is at a right angle or greater from the system origin, the circle is gone.

Any thoughts on the issue would be much appreciated. Thanks!