To expand on @RicoPajarola's comment, this is almost definitely the software not properly handling files with long (or lowercase / etc.) filenames on a FAT filesystem.
Originally, the FAT filesystem only supported filenames of up to 8 characters (+ up to 3 characters for the extension).
Also - lowercase letters, spaces and unicode weren't supported.
Db is a debugger for the Atari ST and TT series of 68000-family
computers... Db can use any of the ST's character devices for its
input and output, including the screen, the serial port, and the MIDI
port... Db is capable of debugging programs running on one machine
while the bulk of the debugger runs on another.
It lets you view the state of the ...