This event occurs because Removable Storage Management (RSM) and some backup software applications are both trying to control the management of the robotic library. The article "Qlogic Support Solution 12362" had few recommendations about how to solve this problem. The article is no longer available online but this is what it said:
Tape backups are failing in Windows when the Removable Service Manager (RSM) is enabled. The server may be receiving Event ID: 168 errors.
This event occurs because Removable Storage Management (RSM) and some backup software applications are both trying to control the management of the robotic library.
To correct this issue, disable the Removable Storage service, as described in the following paragraphs.
1. Enter Computer Management by right-clicking My Computer and selecting Manage.
2. Expand Services and Applications, then highlight Services.
3. Right-click on the Removable Storage Service and click Stop.
4. Double-click Removable Storage, and set the Startup type to Disabled. Click OK.
5. Exit Computer Management.
The error usually disappears after a Windows restart, but after a while the problem occurs again. In one occasion when the restart was not helpful, I removed the tape device from the Windows Device Manager and restarted Windows. Windows reinstalled the tape device and the error ceased to reappear.