Error in Backup Exec

[Rashed]

Dear All , 

I am having Backup exec 12.0 version . and i am using 7 medias for weekly backup .
i am facing a problem that backup hang on queued and then an error message comes :  Please insert overwritable media into the robotic library using the import command.
Overwritable media includes scratch, blank, and recyclable media. Please note that depending on the current Media Overwrite Protection setting, imported and allocated media may be overwritable as well. Consult the online help for more information on overwritable media.

do you knew what is the reason . 

thank you

[Colin_Weaver]

 Is your media set overwrite protected for 7 days or 6? - needs to be 6 days if you use a tape on a Monday and intend to use the same tape on the next Monday.