I keep my PC on a lot and recently when coming back in the morning I would receive the error message "buffers full - no buffer space available" and could not get on the Internet nor any network folders. I found out if I just logged out, I would be fine in the morning. Then checked if I logged in, but did not open any programs, it would be fine in the morning.
I then just opened IE overnight, no problem. I then just kept Firefox (3.5) open and I would get the error.
I then remembered that I had seen a web page on "how to speed up Firefox" and had changed some network settings a number of weeks back. So I just downloaded and reinstalled FireFox 3.5 and the problem went away. The reinstall retained all my favorites. In searching this problem I found a lot of information, but usually dated from 1995 to 2000. So this was a new problem, caused by changing the FireFox "about:config". Glad it was an easy solution.