Cannot load exchanger medium (Target drive is busy.)

Can any Expert help me.

I got this error on my Data protector when i want to format a new Tape or recycle the tape .

Error as below :

[Critical] From: MMA@sema "HP:Ultrium 2-SCSI_1_sema_dds"
Time: 11/11/2008 8:58:51 AM
[90:63] By: UMA@sema @Changer0:0:0:0
Cannot load exchanger medium (Target drive is busy.)