Follow-up on problems with epsilon-input-file

Hi, I have been trying all sort of un-satisfying changes to my ctl file
to try to use a rectangular epsilon file without success.  If someone is
familiar with this, I would greatly appreciate your help.

What I am doing:

I run the diamond.ctl file from the examples folder of mpb.
I then run the command: mpb-data -r -o eps-r.h5 epsilon.h5 ; this
creates a second file with rectangular axis.
I then try to re-read this file with a slightly modified diamond.ctl
file and run mpb to, hopefully, obtain the same bands.

The problem is whatever I try, I always get the error:

...
Solving for band polarization: .
Initializing fields to random numbers...
ERROR: non positive-definite dielectric tensor
CHECK failure on line 421 of mpb.c: invalid dielectric function

I have been trying modifications of the type cartesian->lattice,
lattice->cartesian on the basis set without success.

Here's the modified ctl file if that helps:

; Dielectric spheres in a diamond (fcc) lattice.  This file is used in
; the "Data Analysis Tutorial" section of the MPB manual.


(set! geometry-lattice (make lattice 
			 (basis-size (sqrt 0.5) (sqrt 0.5) (sqrt 0.5))
			 (basis1 (lattice->cartesian (vector3 1 0 0)))
			 (basis2 (lattice->cartesian (vector3 0 1 0)))
			 (basis3 (lattice->cartesian (vector3 0 0 1)))))

(set! epsilon-input-file "eps-r.h5")

; Corners of the irreducible Brillouin zone for the fcc lattice,
; in a canonical order:
(set! k-points (interpolate 4 (list
			       
			       (vector3 0 0 0)                ; Gamma
	
			       (vector3 0.375 0.75 0.375))))  ; K

; define a couple of parameters (which we can set from the command-line)
(define-param eps 11.56) ; the dielectric constant of the spheres
(define-param r 0.25)    ; the radius of the spheres

(define diel (make dielectric (epsilon eps)))

;; A diamond lattice has two "atoms" per unit cell:
;(set! geometry (list (make sphere (center 0.125 0.125 0.125) (radius
r) 
;			   (material diel))
;		     (make sphere (center -0.125 -0.125 -0.125) (radius r) 
;			   (material diel))))

; (A simple fcc lattice would have only one sphere/object at the
origin.)

(set-param! resolution 16) ; use a 16x16x16 grid
(set-param! mesh-size 1)
(set-param! num-bands 5)

; run calculation, outputting electric-field energy density at the U
point:
(run)

Please help!

Nic