Every time this has happened to me, I have (eventually) traced it to corrupt data on the installation medium.
Mount the CD (or USB stick or whatever), cd to /media/whatever, and run:
md5sum -c md5sum.txt
Every time this has happened to me, I have (eventually) traced it to corrupt data on the installation medium.
Mount the CD (or USB stick or whatever), cd to /media/whatever, and run:
md5sum -c md5sum.txt