Compare and Changed File errors When Backup Exec performs a compare or verify operation, it reads the files on your tape and compares them with the original files on your hard drive. If Backup Exec finds that the file on tape does not match exactly with the file on the hard drive, an error is reported. Media Related Errors Problems with the tape media can cause error messages indicating the tape has not been inserted, contains an invalid format, cannot be read, or cannot be written. Any time Backup Exec reports errors, try a second tape to determine whether the tape itself could be causing the error. If you determine that you have a bad tape, discontinue using the tape immediately.
Most manufacturers offer some kind of warranty, in some cases a lifetime warranty, on tape media.
Contact the tape manufacturer for details. Close all other programs before performing a backup. Disable screen savers and power management features. Make sure you are using the correct tape for your drive. Clean the drive with a recommended cleaning cartridge.