"READ ONLY" is displayed.

If displayed when using the MASTER REC function:
It indicates that the connected USB device is non-writable (exclusively for reading). (E.g., a write-protected USB device)
Operation in such a case is as follows.
-Functions such as HISTORY information writing, MASTER REC function, and SYNC function do not work.
-Category browsing is not possible, and only folder browsing is displayed.

If displayed when loading track:
There may be a problem with the file system of the connected USB device. Use a different USB device or format the USB device.