Open move.wdl in your templates dictory;
Scroll down till you see "function scan_floor()", it´s at ca 80% of the script
search for line
Code:

---

trace_mode = IGNORE_SPRITES + IGNORE_PASSENTS + IGNORE_MODELS + USE_BOX + ACTIVATE_SONAR;

---

and change it to
Code:

---

trace_mode = IGNORE_SPRITES + IGNORE_PASSABLE + IGNORE_MODELS + USE_BOX + ACTIVATE_SONAR;

---

then it shout work... well, I never used the templates, so I really don´t know if this is the function that player_walk uses