Sounds like you have it sorted now, if not and you want to troubleshoot it download a tool called ProcessMonitor (a sysinternals app now owned by Microsoft) and trace the HDD activity in real-time while installing (to verify the file is actually missing). Sometimes with ProcMon running you wont encounter the problem, otherwise you can check the ProcMon log and see if the file is actually missing. My gut feeling is slow network, HDD, permissions or something like that which made the EXE file unavailable to the installer.