The EmpiresLauncher.exe may fail to start when other steam accounts have the SDK installed but not run yet (so there's an SDK-directory but no hl2.exe in those account folders). After that, the SDK successfully starts, but the msgbox keeps appearing at the next start, despite the hl2.exe being present in the current users account. Renaming the SDK directory (or removing) from other account directories which are not the currently logged in user solved the problem. Assumption: The launcher takes the first SDK-named directory it can find (which may not be the current user's dir), and tries to start the hl2.exe from there. But upon SDK-start, the hl2.exe is only generated in the current account's SDK-directory, so the launcher fails again next time. How to reproduce: Create another "source sdk base 2007"-directory somewhere in /steamapps/. Success or failure may probably depend on the sort order, if any, in the launcher.