Take a look at the disks referenced for those errors.
Your boot hard drive is ordinarily Disk 0 or Disk 1, while all other drives have succeeding numbers. I cannot view your file right now because I don't have Excel installed, even though I own a version of Excel...but take a look.
One of the reasons I suggested disconnecting the second drive...is to facilitate finding out what drive those errors are pointing to. If a drive is disconnected and you get errors...it's not that drive.
The errors noted could be referencing your DVD drive...it all depends on how you have them set up.
Solving situations like these..is merely a matter of eliminating suspects...it doesn't really matter what order this is done in, as long as you can decidedly think that "this is not the problem." Connecting drives one at a time facilitates that.
As for why Drive A might disappear because Drive B might be bad...I have no answer for the Why, I only know that it can happen. Which is why connections would be the first thing I check.
You don't have to apologize for asking good questions