How do I DOWNLOAD MP3 Files onto an SP 2GB CARD?

How many files have you copied into the root (i.e. top) directory of the SD Card?

As explained above, there is a limit on the number of files which can be stored in the top level directory/folder (the limit varies from one Card to another, for technical reasons, but is typically an even number).

When that limit is reached, the only way to add further files to the Card is to create one or more sub-directories (a.k.a. sub-folders), and add the files in those sub-directories.

Consult the instructions which came with the Card to see if there is a special name that a sub-folder for storing mp3 files needs to have.