dyn.load() function problem help!

Hi!

I would like to call a Fortran subroutine within R. For doing this, I first 
built a shared library for loading into R under Unix and it was successful. 
But when I tried to load a shared library using dyn.load() function for use in 
.Fortran(), I got an error message. 
The command I input below in R is:

dyn.load("aaa.so")

The reslut is:

error in dyn.load(x,as.logical(local),as.logical(now)):
        unable to load shared library "/home/user/fortran/aaa.so":
ld.so.1: /usr/local/lib/R/bin/R.bin: fatal: relocation error: file 
/home/ymu/ft/aaa.so: symbol _F90free: referenced symbol not found.

Does this mean that the shared library was not built successfully or my 
fortran subroutine has some errors?

Any answers to my problem will be very much appreciated!

Best,

Yunming *^_^*