Mine is still working.
But i guess it is somehow related to Valve Updating their stuff for Linux.
They also fucked up HL1 stuff by changing the path it is installed to.
Just hope and pray that they won't break to much stuff this time.
I guess you allready tried things like launching sdk base 2007 and EP2, restarted steam and maybe even redownloaded some files.
And the other half of that story is that every mod for HL1 has successfully been broken with some major shitstorm going on even in the HL1 and CS forums because some people can't even play their original Valve games anymore even after redownloading them.
See
http://www.moddb.com/mods/cry-of-fear/news/valve-have-broken-every-half-life-modhttp://forums.steampowered.com/forums/showthread.php?s=4d5a92b175c036f7151994ab0a274bc1&t=3080953and similar posts. Although when I checked back right on the day it happened, the HL1 forum was full of those threads claiming it couldn't even be fixed by redownloading - I can only imagine they have been removed to cover up that mess. (and that is not counting all the russian threads that had been posted at that time, which, I assume, all talked about this as well)
I mean that is like your mailman isn't bringing you your mail anymore, not because you have a custom mailbox (which the post office had new guidelines released for all of a sudden), but because he couldn't even find your house anymore because he's trying to fit in the new scene he discovered, where all people are smoking pot and he isn't used to doing it yet.
So as you already figured out what I was trying to say: releasing an update for HL1 on windows, not breaking the original game, as well as any mods just because they want to get with the linux "crowd" that will potentially buy and play it (which will sure be lots of people
)was quite unnecessary.
Breaking stuff with updates isn't anything new and there seems no testing process involved prior to "patch" release, because frankly, if something doesn't work out, the public outcry will tell them soon enough. And isn't particularly new that they also tend to break HL2 and HL2 mod stuff with some random update once in a while.