I have had other reports of this happening, usually when the first CTF map in the rotation starts. It only happens if you have Allow Downloads: On.
Go to Setup, Game Options, and set Allow Downloads: Off.
I use customized bot routes, mostly from Darth Kaan's DDS http://www.perkwerx.com/DDS/downloads.htm
but also from Open Jedi Project for the duel maps. They are server-side so you don't need the file, but some glitch makes clients try to get it, but I have downloads off so it doesn't get sent.