Backups on Small Business Server 2003

I am having an issue with backups using the Small Business Backup software in 2003. The problem is that if it is not a clean tape, it won't backup. How do I get around this? I have 2 separate clients running backups this way,1 is working fine while this other one is not.I can do a manual backup which asks to overwrite the tape but I need this to happen without user interaction.

Please help.

Thanks

Mil