Undo operation could not be performed. The operation is being removed from the undo list.

This message appears when trying to undo an operation and the undo cannot be performed. This could occur because the operation cannot be performed given the current online state. While editing online, Controller Transfers cannot be undone, and therefore these operations are not placed in the Undo/Redo list.

For example, if a rung is modified and the pending rung edit is accepted, the modifications can not be undone. The rung now resides in the controller.