New build has fixed error message on scanning for Steam games. I've compiled a list of games that the Games Explorer can't find on my system using latest build:

Blue Shift: Unlocked
Deus Ex: Game of the Year Edition
Dragon Age: Awakening
Doom 3
Doom 3: Resurrection of Evil
DOOM II: Hell on Earth
Master Levels for DOOM II
Quake II
QUake II: Ground Zero
Quake II: The Reckoning
Star Wars: Dark Forces
Star Wars Jedi Knigh: Dark Forces II

There's about another 50 titles I own on Steam that I don't have the HDD space to install at the moment, so I'll try and post back if I have any issues when I get around to playing them all