"Disk is locked" in MSC mode with Mac OS 9.2

Connecting to Mac in MSC mode. 

Mac OS 9.2 - Fuze firmware V02.02.26F 

The Fuze is recognized and mounts on the desktop, but as a “locked” read-only disk.

It is possible to copy files from it, but not to write files to it.

If attempted the following error message is displayed:

“You cannot copy “_files_” onto the folder “MUSIC” because the disk is locked.”

I’ve rooted around but can’t find anyway to unlock the disk.