custom particles vanishing abruptly just before exiting camera's frame

hi everyone,

got stuck with something!

i have a TC particular setup... made the particles freeze with the physics factor and prerun value... and i am using custom particle to make a 3d grid and make my camera simple pass through these particles.
everything is as desired but:
however whenever a particle is close to camera... it suddenly disappears instead of gradually passing off the frame.
this is happening more is the particle is coming head on to the camera.. the ones which are a bit away from the centere of the camera are stayig a bit longer. but even they are popping off abruptly.
my visibility option newar values are at minimal 1 for visibility and 1 for fade out.

please need help urgently!

thanks!
manu



MG