Steam won't load the SDK

[Cyanide]

Every time I try to load the Source SDK from the play games menu it give me an error saying:

MountFilesystem( 221 ) failed: SteamMountFilesystem(1112,221,0x451fbfc=,0x451fd0c) failed with error 114: Cache needs decryption

I've tried deleting the SDK content twice and downloading it again, twice. Nothing has worked. The SDK worked fine after the last update. Now it will not work at all. Has anybody else had this problem? Does anybody know what I could do about it?

 

[Cyanide]

Ok, I discovered that Steam decided that HL2 shouldn't auto-update, without informing me of this decision. Therefore, it would not decrypt the SDK content. Problem solved.