it's normal, you will see E every time you expand DAE's with empty slots. Absolutely put the fillers back in, they protect from dust, air flow ..etc
I just populated a new DAE with 8 2TB drives.  The remaining open slots are telling me they were "removed".  We will populate the remaining bays later.  How do I acknloweledge or get rid of the "E" displaying because the bays are empty, or is this something I'm going ot have to stare at for the next year?  Thanks....
Unsightly "E" displayed in Navisphere