With firmware 6.00 in a Netscreen SSG5, I encountered an odd bug where available sockets for the management web interface run out, because they're not being freed properly.
Rather than rebooting the thing every once in a while, there's a way to free used sockets through the console.

Your best bet is to attach a serial cable to a server or something and use HyperTerminal (or another terminal application) to access the console of the Netscreen.

Once logged in, use the following to get a list of sockets in use:

get socket

This shows a list of in-use sockets, along with their ID. Sockets with the IP address of the Netscreen on port 80 will be the ones you want to clean up, along with their IDs. The ID can then be used to clear it.
You can clear a socket by punching in:

clear socket id ##

Replace ## with the ID of the socket you want to clear.

Special thanks to the support desk of Juniper for this solution.