The Motif, DGX, and other Yamaha SmartMedia keyboards are limited by the DOS-based file format of the SmartMedia cards to accepting only 99 files in the root directory, regardless of size. The workaround is to create a directory in the root directory from your computer's Yamaha software and place the files in this directory, which should have a much higher file number limit, and allow you to fill up the media card with your files.

A directory counts as a file, so if you are currently at the 99 file limit, you will have to delete at least one file to create a directory.