I get a "full" message but it is not full

Try this:
4 Formatting the Recorder (FORMAT)
If you format the recorder, all function settings will return to their defaults.
All files stored in the recorder will be deleted.
If you have important files that you want to save, connect the recorder to a computer and
transfer those files from the recorder to the computer before formatting the device.
1 Press the MENU button.
2 Press the FF or REW button to choose “FORMAT”.
3 When the PLAY button is pressed, “nO” is displayed.
4 Press FF or REW to select “yES”, and press the
PLAY button.
After “ARE yOU SURE” is displayed, “nO” will be displayed.
5 Press FF or REW to select “yES”, and press the
PLAY button.
“DONE” displays when formatting ends.
s It may take up to several tens of seconds to finish the initialization. Do not remove the battery or detach
the battery compartment from the recorder during that time. Otherwise data may be damaged.
s Never format the recorder from a PC.
s When the recorder is formatted, all the stored data, including locked files, are erased.