Occasionally when switching between betas or reverted to a non-beta version of a game on steam the steam game state becomes corrupt. When this happens you no longer can update the program. You can select different betas but nothing will happen.
Following this solution is on your own risk. Do not blame me when it f*cks up your steam configuration.
You must be online with steam. Do not continue if steam is in offline mode.
Make sure you have your steam account info (account name and password) stored somewhere, because these will also be reset.
First make a note of your steam settings. In steam go to the 'Steam' menu and select 'Settings'. Make a note of all your settings on all of the settings pages ('Account', 'Friends', etc..). It might be useful to make screen shots.
The following must be done for all the programs (games) you have installed through steam. Go to the property window of each program (game) and make a note of the tabs (at least the following: 'General', 'Updates', and 'Beta').
If you are in a closed beta and you do not have the password somewhere then do not continue.
Open the windows explorer ('My Computer') and paste "steam://flushconfig" into the address bar and hit <Enter>.
Steam will start and a 'Steam - Reset Configuration' popup will ask you 'This will reset your local Steam configuration and you will need login to Steam again. Do you wish to continue?'
This is your last chance to stop!!!
If you want to continue then hit 'OK' else cancel.
Log into steam with your credentials.
Go to the Steam settings and verify all the settings (which you made notes of in the above steps).
Then check the settings for all installed programs/games. Closed beta passwords must be re-entered.
On this moment download from updates might already start.
Go to the game that did not want to update and verify the local cache.
And now hopefully everything should work again.
I wish you luck.