Open Steam and then hover over LIBRARY.
Choose TOOLS.
Scroll down to Source SDK Base 2013 Multiplayer.
Rightclick on Source SDK Base 2013 Multiplayer.
Select Properties.
Click the BETAS tab.
Under "Select the beta you would like to opt into:", select "beta-test".
Now click Close. This will solve the error "Could not load library client" message when starting the game.
Choose TOOLS.
Scroll down to Source SDK Base 2013 Multiplayer.
Rightclick on Source SDK Base 2013 Multiplayer.
Select Properties.
Click the BETAS tab.
Under "Select the beta you would like to opt into:", select "beta-test".
Now click Close. This will solve the error "Could not load library client" message when starting the game.