Game Problem: Spectator Mode works but cannot join server

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=21

If you can spectate a game but are unable to connect and play, the #1 cause is the firmware in your router.

Usually if you have this problem you can connect and play on insecure servers but not secure (VAC) servers.

If you have a stand-alone router (that is, one not built into your modem), completely bypass your router and plug directly into your modem and see if you still have this problem.

Linksys BEFSR11, 41 and 81 routers seem to be causing this a great deal with the latest firmware version available from their website. If you have the BEFSR11 or 41 router, you need to run the 1.45.7 firmware to solve this problem. The current firmware version that Linksys has on their website: (1.45.11) and some older versions (before 1.45.7) of the firmware can cause these same problems. You can download the known good Linksys 1.45.7 firmware for both the BEFSR11 and BEFSR41 V2 routers at:

ftp://ftp.linksys.com/pub/befsr41/befsr_fw_1457.zip

ActionTec DSL Modems, which have no firmware update available, also have this problem and the modem itself needs to be replaced. Please check this thread about Actiontec problems:

ActionTec Router Problems Thread

http://forums.steampowered.com/forums/showthread.php?s=&threadid=95274

Other Measures required:

1. Disable QoS and uPnP. You need to go into the router and disable UPnP and QoS if it's there, and you should only have TCP/IP checked in the network properties for your Internet connection. 2. Disable Wireless Zero Service (included in Windows XP). You can access these settings in Control Panel > Administrative Tools > Services.

There is more information here: http://www.dslreports.com/faq/6891