Using Particle filter with stereo depth scans

[Singh-sid930]

I am trying to use stereo depth cameras and convert the depth images into fake laser scans to the Particle Filter.
the depth image ofcourse is just in the front so the view is quite constrained.
I get a 1280 ranges with step angles of 0.6 degrees for HD720P and 672 for VGA
I believe I should be downsampling by smaller factor to compensate for the constrained view. However if I Try to make the angle step too low in the configuration file (4 to be exact) it spits out a bunch of

error: invalid argument

between iterations messages.
Is this supposed to be happening?
Also, is there a limit to how low we can go with the angle step for downsampling?