Hammer problem: materials not found, but still show up

I've got a persistent problem with Hammer Editor, and it's happening to any mod I create.

I've got a test mod set up with all default settings, based on HL2 ep2, Source 2007. All the HL2 materials show up in the Texturing tool, but when I run the map, I get [code]material "brick/brickfloor001a" not found.
Material not found!: BRICK/BRICKFLOOR001A[/code]
... on EVERY material. And yet, the map still runs. The lighting doesn't get processed, but the walls are all textured. Static props I place are also not found, and don't show up, but placed weapons do.

I've been through all the config settings in 'gameinfo.txt' and the Hammer Options, but nothing makes a difference. Can anyone suggest possible fixes?

I would guess this has something to do with the latest update mucking up a bunch of the editor configuration. If it is, Valve should release a fix sometime soon.

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Now remember kids. Asking questions is a good way to get censored by the government.

I've searched through the Steam forums and the Source wiki, and I didn't find any reference to similar problems, so I wonder about that. If it were, wouldn't other people be having the same problems?