Hi all,
Thought I'd contribute too
When I upgraded to Windows 7 and ditched my evil resource hog A/V for something better I started to get this error too. Turns out I was loading ET and connecting to the map before PB had a chance to fully start up (my fault for having a -then- fast computer).
When you type in console '
\pb_myguid' you should see your PB Guid (i.e. proving you have one) and your ET Key (only if you're not connected to a server at the time).
Turns out, when I had a kick, I just ran that to check I had a valid GUID then reconnected and all was fine.
Try it, it's similar to Ernie's issue, but not quite as complex a remedy (and easier to remember too!)...
Join server...
--> If no kick, great
--> If you're kicked, wait 10 - 15 seconds
----> Bring down console and run '
\pb_myguid' to check you have a valid GUID and ET Key
----> It no GUID or key then something's wrong with your installation of ET or PB
----> If you have a valid GUID then run '
\reconnect' to reconnect
----> Still a problem then you don't have the same prob as me
----> If you reconnect just fine then next time you connect, if you're kicked for the same reason, just wait a few seconds and try a '
\reconnect'.