Sounds like you need to format the SD card in your machine. The manual shows you how to do this or you can view a YouTube video tutorial that walks you through the full format procedure. (search: Tutorial on How to Format SD card with TASCAM DP24 DP24SD DP32).
I just bought a used 32SD the original SD card and manual was missing and could not be found.
I would like to get a copy of the demo song that comes with the 32SD to work with while learning. Tascam does not offer it for download, and I have been unable to find a copy or download ANYWHERE. Anyone by chance be able to offer me a copy so I can start learning?