If you receive error messages during decompression, you may have
either not downloaded the entire file, have downloaded a bad
file, or received CRC errors during decompression. Read all the
error messages, and this will tell you what the problem is. If
your decompression program complains of missing archives, you are
probably missing some of the release files. To test your
compressed files for CRC errors, highlight all of the compressed
files within your decompression program, and hit the Test button.
If the program reports CRC errors, the extracted file is corrupt
either b/c of archive damage or problems with hardware. If an
archive is damaged, but has a recovery record, you may try to
repair it, otherwise it is impossible to restore the damaged
data.
-ISONews tutorial