The problem might be with your rule file. When you use GRASS through QGIS, it will do something similar:
- Gather input parameters from you with a dialog box.
- Initialize a command line GRASS instance.
- Import the input file in a temporary GRASS location.
- Execute a script with your parameters.
- Export the result.
- Draw the result on canvas (if specified).
In your custom rule file there is a little script, which will initialize
r.reclass with other parameters than QGIS has collected from you. It will search for declives_map, however either it hasn't been created yet, or it has been created, but with other name. Leave the parametrizing to QGIS when you invoke GRASS from it. The correct rule file in your case is the following:
0 thru 2 = 10
2.001 thru 6 = 9
6.001 thru 12 = 5
12.001 thru 18 = 3
* = 1
It will create the reclassified map without a single problem.