If a security rollup or security update for MFC (such as KB2538242) was previously installed on the system, running the base 2005 SP1 installer might trigger a generic error or immediately close.
Alex found the forum post late at night: a single line in a long thread — "download link file vcredistx862005sp1x86exe". It looked like a relic from a different internet, typed without spaces, like a password or an incantation. He clicked. download link file vcredistx862005sp1x86exe