Media mount failed 0x800706be 2147944126 the media operation was terminated by the user.
This error can occur if Backup Exec (tm) has lost communication with the device.
Disabling the device, deleting the device, and restarting the Backup Exec services will force Backup Exec to re-scan the SCSI bus for devices, and re-establish communication with the Tape Device.
Try Following the steps below:
1. Right click on the device and disable each tape device that is not needed: (in this example an autoloader is being deleted)
Figure 1

2. Once it is disabled right click again and delete the device:
Figure 2

3. Respond to the pop message that is seen
Figure 3

4. Restart all services for backup exec with the Backup Exec Services Manager
Figure 4

5. The device should be displayed.
Note: If the device is not present, see the Related Document "How to troubleshoot issues with the "Robotic Library" and "Tape Drives" in Backup Exec (tm) for Windows Servers.
6. Edit the backup job to use the new device