You will receive this error from (among others) Data Protector if the D2D/Tape unit has gone offline, or is not reachable from the machine controlling it. Normally the Data Protector cell manager. In Windows 2008 server you can make sure that Windows is connected correctly via the iSCSI Initiator which you can find in the Control Panel.
If you recieve the error message:
Cannot load exchanger medium (Target drive is busy.)
From Data Protector Manager (or from the backup reports), you have a tape “stuck” in your tape station. This is something that can happen for example if the tape station looses connection to the software using the tape station, (for example a crash on the server) and the software is not setup to automaticly correct the issue itself.
If you want to eject the tape in use you will normally find a option for it on the tape station itself. But a good thing to do is to set up Data Protector to automaticly eject a tape that has taken over a drive.
1) Start Data Protector Manager GUI
2) Select Devices and Media
3) Right click on the library, select properties
4) Go to Control Tab, and select “Eject medium” under the busy drive handling topic