Could not load library client

I've just downloaded the game via Steam and noticed the "Could not load library client" error popping up after a short time after the game was loading.

I've read on other threads that I need to download the Source SDK Base - Orange Box on the Tools section. I had it downloaded for some time under the name Source SDK Base 2007 but it still shows the same error when I launch the game.
I know I sound noobish but I really can't figure out what to do to make this work. Any help would be appreciated.
I also want to mention that I have the old Empires 2.24d downloaded from the game site because I forgot I had it. Is this part of the problem?

Cheers.

 

No it does not, though I could play with no problems the version downloaded from the main site.

 

Then we'll remove the version on main site to avoid confusion. Next Steam version displays error message for processors with no SSE2.

 

Thank you for the reply. I guess I'll have to get a better PC to play this cool game.