After downloading, check the md5sum to make sure the ISO is not corrupted.

In Windows, simply drop the ISO (navigatrix.iso) on md5sum.exe downloaded from here: http://www.etree.org/md5com.html.

Compare the number returned. It must match the MD5SUM found on the Download page. If it doesn't match you get to have the same fun over again.

In Linux open a terminal and execute; md5sum /location/of/navigatrix.iso

Compare the number returned. It too must match the MD5SUM because it's the same process as above.

Good luck.