If the error is only happening with disc 3 so far, I would recommend you do an install with little to no scenery to get flying while we investigate the disc further. A no scenery install will only use DVD 1 so we can by pass the trouble with DVD 3.
Next, please try a couple tests with the problematic DVD:
1. Can you copy the file
X-Plane 11/Global Scenery/X-Plane 11 Global Scenery/Earth nav data/+20-010/+28-010.dsf
from the DVD to ANY place on your hard drive, like the desktop?
2. Can you copy it FROM the desktop to the final install location?