MachFive needs to see a certain file hierarchy to be able to use a preset and it's samples.
Check your MachFive™ Sounds Folder and make sure it has this file structure.
Soundbank.M5b > Backup, Performances, Presets, Samples.
Presets > preset.M5p.
Samples > sample.aiff OR sample.wav.
Your soundbanks should end in .M5b and presents in .M5p.
It is important not to have extraneous characters other than alphanumberics as UNIX
reads slashes and periods as a directory or file type.
You can rename your soundbanks.
This is the main reason you may be getting error messages when loading samples.
Second would be if you do not have enough RAM to load the desired preset.
Remember, your operating system and host application, along with MachFive, requires
memory resources so installing as much RAM as possible will help in your overall performance.