RCA 1501 memory full

Question

I have an RCA Lyra TC1501

I have deleted all downloads, restored factory setting and even pressed the reset button on the back in an attemp to free up memory space.

I usually download audio books to listen to and have deleted them (or think I have since nothing shows up on the player or files when plugged into my mac)

Now when I download something onto it it says there is not enough space to transfer the file to it.  The sytem info on the player shows Free/Total 23M/995M.

Is the problem stemming from me using a mac or is it user error?

Can anyone shed some light on how to fix?

Thanks in advance.