Add Grid Values to Points

Hello to everybody,

I?m trying to use the SAGA tool "Add Grid Values to Points" in R using the RSAGA package 
("shapes_grid", 0) but there is an error message I can`t figure out.:

rsaga.geoprocessor("shapes_grid",0, list(SHAPES="test.shp", GRIDS=list("slope.sgrd", 

"aspect.sgrd"), RESULT="add_grid.shp", INTERPOL=0), env=myenv)

SAGA CMD 2.0.3
library path:   C:/Programme/saga_vc/modules
library name:   shapes_grid
module name :   Add Grid Values to Points
author      :   (c) 2003 by O.Conrad

error: executing module [Add Grid Values to Points]
Usage: -silent -SHAPES <str> -GRIDS <str> -RESULT <str> [-INTERPOL <num>]
  -SHAPES:<str>         Points
        Shapes (input)
  -GRIDS:<str>          Grids
        Grid list (input)
  -RESULT:<str>         Result
        Shapes (output)
  -INTERPOL:<num>       Interpolation
        Choice
        Available Choices:
        [0] Nearest Neighbor
        [1] Bilinear Interpolation
        [2] Inverse Distance Interpolation
        [3] Bicubic Spline Interpolation
        [4] B-Spline Interpolation
'add_grid.shp' is not a correct numeric value for option 'INTERPOL'.

I can`t explain why R is trying to understand the expression "add_grid.shp" as the 
Interpolationmethod even though it is previous to the INTERPOL expression in the 
command.

Any ideas?
Thank`s a lot.

TIM

Dipl.-Geogr. Tim H?ring
Sachgebiet Standort und Bodenschutz (SG 2.1)
Bayerische Landesanstalt f?r Wald und Forstwirtschaft
Am Hochanger 11
D-85354 Freising