I did also 2 tests with 4 browsers in a LAN. First time with Firefox 3 and second time with IE7. I didn't get any errors. I checked with the Linux command "top" the performance load on the server: ~3% CPU
Later I made the same test on a small Linux PC and I got some errors, but the performance load according top: 100% CPU, while mySQL and top where using most of it. I didn't check the mySQL log. But I think thiscould be the problem.
For best results, use the Firefox browser..