AS2000 cannot overwrite same media name

[yumanho]

I am using AS2000 Adv Edition. Recently, an error have occurred during backup.

I formatted 4 media with the same media name and I scheduled a job to backup to this 4 media with the options:

Option for First Backup Media - Append to Media
Option for Additional Backup Media - Overwrite Same Media Name, or Blank Media

This job backup successfully in the first 3 media with the same media ID and 1-3 sequence. After the third media was full, the job have tried to overwrite the fourth media but failed with error message &quot;Please mount <Media ID> seq 4 and try again.&quot;

Does anyone get the same experience? How can I solve this problem? Please advise! Thanks!