fortran_parse error in the fortran_autodoc module for a basic example

[PauJuan]

Hi,

I am trying to set a minimal working example for fortran_autodoc. make html works when no files are added to the project. If I add a simple file such as:

module constants  
implicit none 

   real, parameter :: pi = 3.1415926536  
   real, parameter :: e = 2.7182818285 
   
contains      
   subroutine show_consts()          
      print*, "Pi = ", pi          
      print*,  "e = ", e     
   end subroutine show_consts 
   
end module constants 

The file name is test.f90 and it is picked up by conf.py. I get the following error:
Handler <function fortran_parse at 0x00000166EC1CFCA8> for event 'builder-inited' threw an exception (exception: 'C')

I tried with the test files in the repository as well but I always get the same problem. This is independent to referring to them in index.rst. I imagine it is something to do with my setup, but I didn't find the traceback helpful at all. Perhaps somebody has come across it before?

Many thanks for your help.