Yeah this is Valve's fault. There is only one solution to this at the moment which is to install a custom configuration.
Copy all of this into notepad:
"Configs"
{
"Games"
{
"Goldeneye: Source - 4.1"
{
"GameDir" "c:\program files\steam\steamapps\sourcemods\gesource"
"hammer"
{
"GameData0" "c:\program files\steam\steamapps\sourcemods\gesource\goldeneye.fgd"
"GameData1" "c:\program files\steam\steamapps\USERNAME\sourcesdk\bin\source2007\bin\base.fgd"
"TextureFormat" "5"
"MapFormat" "4"
"DefaultTextureScale" "0.250000"
"DefaultLightmapScale" "16"
"GameExe" "c:\program files\steam\steamapps\USERNAME\Source SDK Base 2007\hl2.exe"
"DefaultSolidEntity" "func_detail"
"DefaultPointEntity" "prop_static"
"BSP" "c:\program files\steam\steamapps\USERNAME\sourcesdk\bin\source2007\bin\vbsp.exe"
"Vis" "c:\program files\steam\steamapps\USERNAME\sourcesdk\bin\source2007\bin\vvis.exe"
"Light" "c:\program files\steam\steamapps\USERNAME\sourcesdk\bin\source2007\bin\vrad.exe"
"GameExeDir" "c:\program files\steam\steamapps\USERNAME\Source SDK Base 2007"
"MapDir" "C:\maps\dev"
"BSPDir" "c:\program files\steam\steamapps\sourcemods\gesource\maps"
"CordonTexture" "tools\toolsskybox"
"MaterialExcludeCount" "0"
}
}
}
"SDKVersion" "3"
}
Rename all the instances of "USERNAME" in the file with your Steam account name. If you use a 64 bit OS rename your "program files" directory in each instance appropriately as program files (x64)
Then save it as GameConfig.txt and stick it in your steam/username/sourcesdk/bin/source2007/bin folder