Hm, what about more details?
Ensure the user uses a compatible fmod.dll;
Actually, on vb6 I failed using fmod 3.20a, and fmod 3.70 crashed frequencly with my player)
What functions do you use in your application?
Can be an delayed error, means that the error that caused the crash was some stepts before, and it’s not fmod.dll’s fault.
Best would be, however, built in some debug information (log file) to analyze where your applications crashes (or try it in ide-mode on that client).
Also check sound card, directX version, …
E.g. When using DirectSound Output I also encountered division by zero errors with visual basic after initializing visual basic when using the timer functions), and with an older version the same problem when quitting).
Try also starting from another location (e.g. on XP, my player crashes when started from within the desktop folder)
Try also deleting all settings (inifiles, regestry), and try other output modes your soundcard supports (eventually even Null-Output)
Basically, more information, please, and maybe I can give you better instructions;