Failed to load the default scheme file

(hammer editor related) here's the fix for "Failed to load the default scheme file. The map views may be missing some visual elements"

get SourceScheme.res from one of the GCF files or create a mod, and get it from that.

copy it here: SteamApps\usrname\sourcesdk\bin\resource\

or try here: SteamApps\usrname\half-life 2\hl2\resource\

if this doesn't work, then you could use Filemon from sysinternal's to find out where Hammer is looking for this file and then place it where hammer looks.