gzip: stdin: Input/output error,what does it mean?

I do the following
(1)mount /dev/cdrom /mnt -->okay,will get *.gz file when cd /mnt
(2)cd /tmp
(3)tar zxf /mnt/*.gz
get error like below:
gzip: stdin: Input/output error
tar: Unexpected EOF in archive
tar: Unexpected EOF in archive
tar: Error is not recoverable: exiting now