I think it might have something to do with the map.
Go to steam>steamapps>(account name)>counter-strike source>cstrike>maps
Move all your maps to a random folder that you create (instead of deleting, just in case this doesn't work) and then try to connect. If it says you're missing the map, download them from here >
http://www.cstrike-planet.com/mapsSee how that goes