I’ve noticed the same thing about the last block being unreadable. Me thinks this is actually normal. Is it possible that when the burner finalizes a session or closes the CD it writes a block which can’t be read, essentially telling the reader that there ain’t no more stinking data on the CD so don’t bother trying to read beyond this point?
That could explain why if you don’t finalize a session or close a CD that the disc is unreadable by CD-ROM/DVD-ROM drives but is still read/writeable by the CD burner since you can add additional data to the disc (i.e. multisession).
I have scanned a few of my CD-R/RW discs (made by different buners) and they all have that unreable block on the end, yet when I test the integrity of the data (in the form of .zip files) on the CD they all come up good, and you know if just one bit is wrong in a zip file it will not pass a CRC check.
I also scanned some pressed CDs and NONE of them have the unreadable block on the end. So it must be unique to CD-R/RW discs so as to tell the reader the length of/end of the data on the disc otherwise the reader would just continue to read to the end of the rated capacity of the CD-R/RW even if there was no data written there.
Just my two cents worth.