I haven't heard of this error before.
Just try waiting or go to the http://www.counter-strike.net place and ask them for support.
I'm sure it's just a common error there as it is a unique error here.
Try to delete(or rather move to make steam not to see it) the "c:\program files\steam\steamapps \counter-strike source" folder. Steam should remake this folder from the gcf files.