Hi Gilly,
The 'long' names of the songs on your SD Card are stored in a file on the card which is called 'KN7000MN'. It is probable that this particular file has become corrupted

However, there is a chance that you can recover the data which is normally present within that file.....
Located on the SD Card, there is a backup of the data which is normally contained in the KN700MN file - this file is called KN7000MN.BAK

Depending on how 'Savvy' you are with a computer, it is possible to recover the data from the KN7000MN.BAK file and copy this to the corrupted KN7000MN file, thereby restoring the 'Long' filenames in a single operation. This process assumes that the KN7000MN.BAK file has not been corrupted....

If you want to try this, post back and I'll send you the procedure. You will need either a USB SD Card Reader/Writer or a Laptop/Computer with a suitable SD Card slot.