You can’t change the startup disk to the selected disk?
The first thing I'd try is resetting the NVRAM:
Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R. Turn on your Mac.
Press and hold the ⌘+Option+P+R keys immediately after you hear the startup sound.
Hold these keys until the computer restarts and you hear the startup sound for a second time.
Release the keys.
...and see if that solves your problem. If it doesn't, I'd start worrying about a hardware fault.
I had the same issue when I was adding a new external HD to boot from. My original boot drive started giving me this error. It was still usable, and I could boot from it if I held the option key down during startup and selected it, but could not select it from Sys Prefs without getting an error. I tried all the Disk Utility things to no avail. It was only when I reset the NVRAM with the cmd, option, p & r solution that everything went back to normal.