kldunload: can't unload file: Operation not supported by device

[KGB]

Hi all:
      I have a problem using kldunload system call to unload my driver module.
      
      BSD# kldstat
   Id Refs Address    Size     Name
    1    6 0xc0400000 906518   kernel
    2    1 0xc0d07000 6a32c    acpi.ko
    3    3 0xc4f0e000 34000    zaptel.ko
    4    1 0xc4f65000 2000     ztdummy.ko
    5    1 0xc4f67000 9000     fxm8apci.ko
       BSD#kldunload fxm8apci
      kldunload: can't unload file: Operation not supported by device
      
      If I use the parameter "-f" with kldunload ,the result is identical.   
      
      Can someone give me advice?
      
      Thanks in advance.