Problem with assigning the address of a function to a LIB-variable

I have written a LIB with the following decleration:

  idata u_char clock_occ;
  idata void (*f_ce)(u_char stat);

I use it in the LIB in the way as:

  clock_occ = 1;
  f_ce(TRUE);

so far, no problem, I compile it -> ok:

I add the LIB to my project and use it like:
 
  extern idata u_char clock_occ;
  extern idata void (*f_ce)(u_char stat);

  void SetChipEnable (u_char stat)
  { ... }

  void main (void)
  {
    clock_occ=0;
    f_ce = (void *)SetChipEnable;
  }

-> now I get at the use of "clock_occ" no error, but at the use of "f_ce" I get the warning "1" + "2" (unresolved ex. sym.)

Why?

Many thank's for help.

Norbert Christof