vncserver xlib error

Hello!
Im running tight VNC on Red Hat Enterprise Linux 4.0.
How can I increase the number of X clients that I can run
in a VNC session?I need to run aproximately 500 programs in one VNC session,
but at this time I can only 236 -> i've tryed to launch 250 xclock's in background
and when it comes to 237, the error Xlib:Maximum number of clients reached
comes out. Please, help me on solving that issue!