First try restarting steam. By restarting i mean type in your username and pw. Then try getting in a server. This has worked for me before. If nothing else, read the below link.
lolz thats funny. just happened to me, heres what you do: go into my computer > into your C drive > Program files > into your steam folder > and delete a file called clientregistry.blob
and now you will be able to join servers again. hope this helps
I had this same issue tonight. I had to exit Steam then delete the following files from my Steam folder. When I restarted Steam, it "patched" itself and everything was good to go.
If restarting Steam does not resolve the issue, please exit Steam and delete the following files from your Steam directory:
* Steam.dll
* SteamUI.dll
* Rename the ClientRegistry.blob
I went through this today.
Deleting the clientregistry folder did the trick. After deleting it I did have to completely shut down Steam and restart it. Worked fine after that.