Replaced MacBook Pro's Hard Drive...
 

Now every time I start up SD it says "Cannot find source volume Macintosh HD" even though I named the new internal HD the exact same. "Macintosh HD"

Everything else works fine. How do I stop this error message?

It's because the low-level ID has changed. Cancel the prompt, select some other drive, select the right drive, quit.

Also - once you restart successfully, delete and recreate any schedules.

Perfect! Thanks, J