error with function declaration

[Marcello Vichi]

Dear all,
hope someone can help me with this problem that's driving me mad...

I am currently porting a scientific software for biogeochemistry 
simulations to gfortran. For those of you who are interested in this 
stuff, check www.bo.ingv.it/bfm
Compilation is fine both with Portland, ifort (on linux and mac) and F90 
compilers on NEC SX machines.
However, I get an error with gfortran (linux and mac) when I have 
functions declared in this way

       REAL(RLEN) FUNCTION BESS_EXP(X,LAMBDA,FN)
         USE global_mem, ONLY:RLEN
         USE constants
         IMPLICIT  NONE
...

where RLEN is declared as
   MODULE global_mem
   INTEGER, PARAMETER :: RLEN=kind(1.D0)
...


The reported error is:
       REAL(RLEN) FUNCTION BESS_EXP(X,LAMBDA,FN)
           1
Error: Parameter 'rlen' at (1) has not been declared or is a variable, 
which does not reduce to a constant expression

I've never had problems with the other compilers up to now. I can 
overcome this by declaring the function name in the preamble
REAL(RLEN) :: BESS_EXP
but I have quite many of them, and moreover this kind of declaration 
should be standard since f90

Does anyone have an idea of what I'm doing wrong?


Many thanks in advance

Marcello

-- 
 >>> NOTE THE CHANGE OF ADDRESS AND TELEPHONE NUMBER <<<
Dr Marcello Vichi
Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC)
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Via Aldo Moro 44, 40127 Bologna. Italy
Tel: +39 051 3782631 Fax: +39 051 3782654
Email: marcello.vichi@cmcc.it, vichi@bo.ingv.it
skype: marcello_vichi