My Norton Ghost tray icon has a red circle with a x in it

The icon in the sys tray gets a green circle in it during a backup but when it is completed I get a red circle with an x in it that stays there. Is that OK? Also when I go to Norton Ghost HOME it says I am at risk, that one or more files did not back up successfully but yet the back up said it completed OK. Any idea what is going on here?  am running Windows XP with the latest updates, using Ghost 15, and I am backing up on a external powered USB  hard drive. I am doing two back ups , one for my C drive and one for my D drive, both are internal hard drives.