First, to explain the different states. There are two kinds of “Remove”, one is “Remove” and one is “Force Remove”.
When you Remove a device, it marks the device for removal (Device Removal Pending) and then the next time that device checks in, it will be logged out, and then moved to the “Removed” state. If the device never checks in again, it will remain in “Device Removal Pending”.
Force Remove, has the the same effect as Remove, though it additionally moves the device straight to Removed and also signals the cloud to invalidate the user’s session.
Today, you can do a multiple select for Remove, but you cannot do a multiple select for Force Remove.
The reason you get this error, is that if a device is in Removal Pending, then it’s already been Removed, so doing Remove on this would have no effect.
If you want to Force Remove devices instead of waiting for them to Remove, you need to do this one device at a time. We do have an enhancement planned to allow multiple select with Force remove.