Mavericks 'Invalid' Start-Up Problem

[Loopy C]

Originally Posted by dnanian

Renaming the disk wouldn't cause this kind of problem. It sounds like something lost the NVRam setting for the startup disk. Did Option+Boot show the disk (as opposed to "Recovery")? Cmd+R wouldn't really do anything useful, so I'm a bit surprised that worked at all in this situation...

The 10.9.5 disk is always 'available' as a start-up from preferences...it just hits this problem (haven't done the exact sequence of 'option boot' as again since I had original problem and stumbled onto 'solution' of Command-R, yesterday was only second time I attempted shut down/fresh boot (which I was pushed to risk as I needed to do a Command/Option P/R as I was experiencing 'lags' with my keyboard controlled on-screen volume control).

According to Apple, 'Prohibitory Sign' means system HAS found and recognized the installed OS as a valid OS, but cannot boot from it because of some problem with the system.

It's this 'Command-R' as solution that really throws me. I think when I attempted 'Safe Boot' during initial troubleshooting it reverted to doing a 'Safe Boot' from the 10.8.5 partition so I could never do a 'Safe Boot' from 10.9.5.

I don't know if it would be possible to do a combination of 'option boot' to select 10.9.5 drive, then immediately direct it to 'Safe Boot' from that selection? If so, I then at least have option to maybe run 'Combo Updater' again to fix while booted in Safe while on problematic drive but at this point, I am avoiding the situation of losing my current working system until I feel comfortable with what/why these particular events are and their meaning ...as you said 'Command-R shouldn't do anything yet twice now it has allowed boot!

Thanks for reply ;-)