[ESPResSo] how to specify normal wall?

[Salvador Herrera Velarde]

Dear All,
 
 I am trying to to implement the  wall normal constraints in one of my scripts,  however I run into some troubles.
 
 What I did was:
 # Particle potential ( type 0 )
 inter coulomb $lb dh $dk $rc
 
 set dc1 [expr {0.8* $bl } ]
 constraint wall normal 0 0 -1 dist $dc1 type 1
 
 set dc2 [expr {0.2* $bl } ]
 constraint wall normal 0 0 1 dist $dc2 type 2
 
 inter 0 1 wall normal
 inter 0 2 wall normal
 
 It is supposed that I have the constraints feature activated, but the result is:
 
 excessive parameter/unknown interaction type "wall" in parsing non bonded interaction
     while executing
 "inter 0 1 wall normal "
 
 Could you help me to handle this?
 
 thanks a lot for your time,
 
 Salvador