Hi everyone,
We're aware of the installation / launch error that some customers are experiencing due to the 3rd party GFWL key error.
For the time being, we've had Valve disable the 'missing key' system notification so players can get past the error and get the game to launch.
Background: while the game no longer utilize the Games for Windows LIVE service, we still left in a feature that allowed previous GFWL users to import their old save game progress and Achievements into the Steam version. This necessitated the game to enumerate the old save data by requiring users to login into their GFWL account in order to load the save file and, more importantly, download the Achievement unlock state from Microsoft's Xbox/GFW LIVE servers tied to the user account/save file.
For the reason noted above, the game requires users to install the GFWL client during the initial installation process. Those who have never played the GFWL version of RE5 previously or have no interest in importing the save data and Achievements can safely ignore the GFWL component. However, please do not skip the GFWL client installation. The game may fail to launch if the GFWL client is missing.
The GFWL client login will pop up only when you access the "IMPORT WINDOWS LIVE PROFILE" feature located in the OPTIONS menu.