Yes, the file is in the appropriate folder.
I even tried coding it like so, just in case:
If File Exist("test.mp3")
Load Music "test.mp3", 1
Play Music 1
EndIf
If the file was not being found, this would result in the program running fine, only with no music. However, this results in the exact same error message being directed at the Load Music line.
I did some experimenting and found that it works fine with WAV* files, just not any of my MP3s. Obviously this is some kind of formatting issue, but I can't find any information as to what kind of MP3 format DBPro might actually support.
*I don't want to have to use WAV files for my in-game music due to their poor sound quality.