Most of the results I get are you should re-start Steam and/or your computer. That seems obvious. Others are un-installing and re-installing Steam entirely. These solutions are obviously retarded and probably only work for about 10% of the people experiencing this problem. Good luck.
I think this an appropriate time to post my latest Rage comic.
![](http://sphotos-a.xx.fbcdn.net/hphotos-ash3/552681_471939392834454_1838225820_n.jpg)