The main reason why you get this error is that you or the server is having a problem with the Internet connection. To identify and eliminate the source of the problem you can try the following steps:
- close all extra applications before playing;
- scan your computer for Viruses, Trojans and Worms;
- if you're using a wireless network try connecting with a direct cable and disable Wireless Zero Configuration before playing;
- set cl_updaterate 20 and cl_cmdrate 30 in your console.