This message is displayed when RAM area is in an illegal state due to insufficient remaining power in the internal backup battery.
In this state, the data of drive 2 can no longer be used, so follow the on-screen instructions to initialise drive 2.
Before initialising drive 2, be sure to back up important files. To do this, save this files to drive 1 (Flash-ROM) because files will not be deleted even if there is no more remaining power in the internal backup battery.