You did check the md5sum for the iso image that you downloaded?
I would check the md5sum. If you downloaded the cd/dvd iso then be sure to check the md5sum for the original iso (get the md5sum file with the iso). From the cli;
~#cd /downloadisolocation #cdromiso.iso cdromiso.md5
~#md5sum -c cdromiso.md5 #substitute the correct name to check
If the iso md5 is ok then you should try 'CdromMd5sumsAfterBurning'
This way you will know if the burn was OK!
This will check the download iso with the known md5sum that you also get with the iso.
These links and others can be found at 'Slackware-Links
'. More than just SlackwareŽ links!